LISTING HIGHWAY PARAMETERS For highway ...

LISTING HIGHWAY PARAMETERS For highway geometrics

Towards the development of a common methodology in international highway design.

Author: Robert E. Bartlett

Pre-Release Version 8c April 2017

Listing Highway Parameters - Part 1: Introduction

About the author

Mr. Bartlett is an international consultant with over 30 years of professional experience as a highway and traffic engineer. He has worked with leading companies and organisations in several countries, including Germany, China (Hong Kong), Qatar and the UK. His interests include urban studies, highway engineeering, comparative geometrics and the use of GIS. Mr. Bartlett has presented papers at conferences organised by the EC, the US Institute of Transportation Engineers, the UK's AGI, and others. Countries he has worked in include: Albania, Denmark, Germany, Holland, Hong Kong, India, Jordan, Kuwait, Libya, P.R.China, Qatar, Romania, Saudi Arabia, Switzerland, Tanzania, UAE, Uganda and the UK. Email comments to : [email protected],

Copyright

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

LHP- Highway Geometrics - pre-release 8

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About the author Mr. Bartlett is an international consultant with over 30 years of professional experience as a highway and traffic engineer. He has worked with leading companies and organisations in several countries, including Germany, China (Hong Kong), Qatar and the UK. His interests include urban studies, highway engineeering, comparative geometrics and the use of GIS. Mr. Bartlett has presented papers at conferences organised by the EC, the US Institute of Transportation Engineers, the UK's AGI, and others. Countries he has worked in include: Albania, Denmark, Germany, Holland, Hong Kong, India, Jordan, Kuwait, Libya, P.R.China, Qatar, Romania, Saudi Arabia, Switzerland, Tanzania, UAE, Uganda and the UK. Email comments to : [email protected]


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About Global Transport Atlas Global Transport Atlas is a research project which looks at aspects of highway design and traffic studies in different countries of the world, and which publishes documents on these topics. Sources of information include formal and informal design standards and guidelines published in different languages, research papers, and in-country contacts.


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Table of Contents Cover Title page About the author About GTA Table of contents

1-4

Part 1 - Introduction 1.1 Aim of this document 1.2 General structure of this document 1.3 Associated documents 1.4 Version history

Part 2 - Discussion

2-1

2.1 Introduction

2-2

2.2 What are “parameters”

2-3

2.3 Identifying parameters

2-5

2.4 Listing parameters

2-12

Part 3. Notes on the parameters 1.

3-1

Road type

2. Vehicle type 3. Road users 4. Geometrics 4.1 speed 4.2 controls 4.3 horizontal alignment


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4.4 vertical alignment 4.5 cross-sections 4.6 parking 4.7 junctions 5. Geography 6. Economics 7. Engineering 8. Aesthetics 9. Concepts

Part 4. Lists of parameters

4-1

1. Road type 2. Vehicle type 3. Road users 4. Geometrics 4.1 speed 4.2 controls 4.3 horizontal alignment 4.4 vertical alignment 4.5 cross-sections 4.6 parking 4.7 junctions 5. Geography 6. Economics 7. Engineering 8. Aesthetics 9. Concepts


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Part 5 - Definitions

5-1

Part 6 - Annexes Introduction Annex 1 Glossary (excerpt) Annex 2 List of references (excerpt)


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PART 1 - INTRODUCTION

Contents of this section:

1.1

Aim of this document

1.2

General structure of this document

1.3

Associated documents

1.4

Version history


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1.1 Aim of this document Suggests there should be a simpler way to document the principles behind the geometric design of a new road.

Wherever you travel in the world you will find many different types of road, and different types of vehicle which use them. The road you are using might be a motorway or a country lane, the vehicle a truck-trailer combination or a bicycle. If you are planning a new road you will also find many different documents which give you advice - and perhaps instructions - on how to design it, and how knowledge of the types of vehicle which will use your road can affect your decisions. These documents appear in different languages, and cover different political and administrative areas such as countries or urban areas. In the USA there are documents issued at a national level, by individual states, and by individual cities or special interest groups. So far as language is concerned, many very useful documents are published in languages other than English- those by Germany’s FGSV (in German) and by Chile’s Ministry of Public Works (in Spanish) are just two examples. But differences in administrative area and differences in language have nothing to do with the design of roads. After all, a truck driver travelling between France and Germany does not have to stop at the frontier between area and language and change his vehicle for a different one.

Documents on road design - from local guidelines to international standards to textbooks - all approach the topic of highway design differently; Even when published in the same language and country, road design documents use different terms for the same engineering feature such as speed; and they hide the details of the feature in a puzzle of pages and an impenetrable fog of words. If we can eliminate these problems of language, boundaries and terminology then the people who prepare design documents would be able to present their suggestions in a consistent manner. This would allow readers to compare these ideas and decide which ones were the most promising for their own project. It would also be possible to reduce the presently very large number of highway design documents, and so help make road design a more efficient exercise.

Parameters - one way to simplify matters would be to begin with the building blocks of highway design, with what we can call "parameters". There are more than a thousand parameters involved in just the geometric design of roads, and many more for the materials aspects of road design. This document therefore is limited to a discussion of geometric design parameters, Examples of these include road type, lane width, and vertical gradient. The basic argument is that once designers


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Listing Highway Parameters - Part 1: Introduction agree that, say, "lane width" is a useful parameter - and once they can agree on what they mean by "lane width" - then people who issue road design standards can structure them in terms of these parameters, and people who use the standards will be able to compare different solutions and values for a particular parameter. This means that there are three key steps for any parameter identifying it, deciding on just one term to refer to it, and providing a definition of it. Once design standards use a consistent approach to identifying and defining a parameter, road designers will be able to search design standards for different solutions or values for the parameter, and then to select the most convincing one as the current best practice solution for their project.

The aim of this document is to present a structured list of all the parameters involved in the geometric design of roads. The document also includes a discussion on the problems of highway geometrics and parameters, some notes on the main parameter groups, and examples of how to present solutions for individual design parameters.


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1.2

General structure of this document

Lists the groups into which parameters involved highway geometric design have been sorted, and summarises the various parts of this document,

Parameter groups This document looks at the parameters involved in highway geometric design. Early work quickly identified several hundred parameters. It is easy to lose an overview with so many, and so it was decided to gather the parameters identified into a small number of groups. The parameters in each group have a common theme, as their names suggest. Even with this step, one group still had a large number of parameters, and so it was further divided into a number of sub-groups. The groups and sub-groups are: 1. 2. 3. 4.

5. 6. 7. 8. 9.

Road type Vehicle type Road users Geometrics 4.1. Speed 4.2. Controls 4.3. Horizontal alignment 4.4. Vertical alignment 4.5. Cross-sections 4.6. Parking 4.7. Junctions Geography Economics Engineering Aesthetics Concepts

Structure of this document This document has seven parts. The first part is the present, “introduction” section.The six other parts are:


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Part 2 includes a detailed discussion of what geometric parameters are and the problems associated with identifying them. Part 3 - has notes on each of the nine parameter groups, and on the seven sub-groups of "geometrics" Part 4 - includes starter lists of parameters for each group and sub-group Part 5 - list of definitions for this document Part 6 - annexes, with details from a glossary and details of references


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1.3

Associated documents

This document is one of a wider series of publications and extracts,

Listing parameters may be a useful step in simplifying a study of highway geometrics, but by itself does not take designers into very much engineering detail. More information is contained in a number of associated documents. Some deal with the topic of “parameters” in general. The layout and content of others vary with the various parameter group they refer to - although their general structure is still the same for each group.

General documents Table of parameters

A structured list of parameters. The parameters are sorted into groups and sub-groups, and into levels of importance (see later). At least one source reference is given for each parameter.

Glossary of parameters

A document with one or more definitions for each parameter. The definitions may be contradictory.

List of references

A list of source documents, with details such as publisher, language, country of publication and so on

And

Specific documents List of solutions

List of different solutions for a particular parameter, with notes of the standard or document each was taken from

Solutions

Documents with detailed information on one specific solution. Usually one- or two-pages long, they are usually in English, although the source publication may be in another language.

Other related documents


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Listing Highway Parameters - Part 1: Introduction Road Design Standards

Country-by-country listing of important and interesting documents on designing for road transport - both motorised and non-motorised. There are also separate lists of multi-country documents and topic documents.

Discussion papers

Documents which look in detail at a particular geometric design parameter, such as minimum horizontal radius.


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1.4

Version history

A record of the updates and versions of the published versions of this document,

Listing parameters may be a useful step in simplifying a study of highway geometrics, but by itself does not take des Version history Revision

Date

Details

Notes

LHP pre-release 8

March 2017

First pre-release version of the full document

Limited issue edition, circulated for comments


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Listing Highway Parameters - Part 2: Discussion

PART 2 - DISCUSSION


2.1

Introduction

2.2

What are “parameters”

2.3

Identifying parameters

2.4

Listing parameters


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2.1

Introduction

This section discusses what is meant by the word "parameter". It goes on to talk about how parameters can be listed, that some parameters may be more important than others, and that it is possible to create not just a list of parameters but some sort of structured list of parameters.


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2.2

What are “parameters”

Explains what this document means when it uses the term “parameter” in the context of highway geometric design..

Searching for examples One way to explain what parameters are is to search the Internet for dictionary definitions of the term. Such a search might produce results such as: "A numerical or other measurable factor forming one of a set that defines a system or sets the conditions of its operation" https://en.oxforddictionaries.com/ And "Definable, measurable, and constant or variable characteristic, dimension, property, or value, selected from a set of data (or population) because it is considered essential to understanding a situation (or in solving a problem)" http://www.businessdictionary.com However these results do not specifically relate to highway design. Another way to find out what the term “parameter” means would be to search published documents on highway design for paragraphs where the term is used. Examples found include: "A compilation of the 85th percentile values of the various parameters of the vehicle type being designed for, e.g. length, width, wheelbase, overhang, height, ground clearance, etc., and not a commercially available vehicle". Ref. 2247, South Africa, 2015 And

"Included under location and geometry of site are parameters that are likely to vary along the entire length of the road being considered. These parameters are radius of curvature and superelevation of the road, longitudinal gradient, altitude and shade". Ref. 834, UK, 2007

The results give a general understanding of what the term means in the context of road design, even though they do not include a formal definition of it. But this sort of search can produce a number of results which may not mean the same as "parameter", or which might be special variations of it, for example: ● Design parameter (ref. 929) ● Basic design parameter (ref. 138) ● Geometric design parameter (ref. 1038)


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Listing Highway Parameters - Part 2: Discussion A search of technical documents will also produce terms which, although they use different words, may mean the same as “parameter”. For example, the book “Road engineering for development” (ref. 856) has a section headed “Geometric design elements”. The section lists a number of these elements which “.... must be considered when carrying out the geometric design”. As a matter of interest, the list is structured with elements sorted into three groups: horizontal alignment, vertical alignment, cross-section. Working definition So published documents may include notes on “parameters” which use terms which mean the same thing but use different words, or use the same word but may mean something different. It might then be as easy to begin with a working definition for the purpose of this document, such as: "In the context of the geometric design of roads, a parameter is a definable, quantifiable feature or variable which influences or sets the conditions of the design" Author


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2.3

Identifying parameters

Works from a discussion of what a road design “standard” is, to identifying relevant standards, and picking out relevant parameters. It includes a discussion on terms and language.

2.2.1 What is a standard Suppose we begin with the idea that - so far as a discussion of road geometrics is concerned - a “standard” is a document which is published by a specialist government department such as the UK’s Department of Transport, a document which contains detailed technical notes on geometric road design, and which may represent required practice. We might also begin with the idea that such “standards” also represent unquestionable best practice and can be followed with little extra thought. Both these ideas are misleading and incorrect, for example because: ● ●

Many non-government bodies publish useful documents on geometric design Government bodies issue documents on suggested practice as well as on required practice

and it is also probably true that: ● Documents on the same topic but published by different bodies often give conflicting advice ● The advice in standards can vary over time ● Standards are not necessarily unique - they can contain material copied from other documents ● Where the advice in a standard does not vary with time, the advice is probably out of date ● Different standards can give different advice on the same geometric design parameter ● Standards can be wrong Here are some notes on such documents: 1. Many organisations publish standards Many central and local government bodies produce publications on the geometric design of roads. They include, in the USA, ● ● ●

The FHWA (Federal Highway Authority) for example with its Separated bike lanes planning and design guide (ref. 2184) the State of Illinois' Department of Transport (Bureau of design and environment manual) (ref.1999) The city of Philadelphia (e.g. the Philadelphia complete streets design handbook) (ref.2333)


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Listing Highway Parameters - Part 2: Discussion Non-government organisations which produce these publications include universities, publishing houses, and special interest groups such as, again in the USA ● ● ●

University of Michigan (Parameters affecting stopping sight distance) McGraw Hill (Highway engineering handbook, 2nd edition) Institution of Transportation Engineers (e.g. Designing Walkable Urban Thoroughfares: A Context Sensitive Approach - an ITE recommended practice)

There are also standards which are published by organisations which cover more than one country. Examples are ● The UNECE (United Nations Economic Commission for Europe) - Trans European Motorway standards and recommended practice, third edition ● United Nations - Asian Highway Handbook

2. The advice in standards can vary over time An example here is the document "A policy on the geometric design of highways and streets", which is published by AASHTO (the American Association of State Highway and Transportation Officials) . The 6th edition of this document was published in 2011. If the advice it contained did not change there would be no need for a new edition.

3. Standards often include material copied from other documents An example of one standard including material from another is volume1 part II of Paraguay's "Normas para la Evaluacion de Proyectos y Geometria Vial" (ref. 895) of 2011 ends with a bibliography. This suggests that the document is based on research and publications in other countries in South America. The bibliography includes references to the AASHTO guideline (1994 edition) and to South Africa's "Geometric design guidelines". This does not mean that the Paraguay document is not a valuable publication in itself.

4. Standards may contain out-of-date information An example here is Dutch road design guidelines for freeways. In a paper on horizontal curves, the authors Broeren, Uittenbogerd, Groot, Ruijs say that "The design of horizontal curves is incorporated in the Dutch road design guidelines for freeways (NOA) and highways (Handbook Road Design). Although the horizontal curve sections of the latest editions of these guidelines are updated, fundamental parameters and parameter values remain unchanged; vehicle and road characteristics research from the 1970s is still the foundation for the guidelines. Since modern vehicles, road pavement surface and driver characteristics can’t be compared to those of the 1970s, fundamental research is needed to determine a representative guideline on horizontal curves". (ref. 2326, Netherlands, 2015) 5. Standards which discuss the same geometric parameters may not be based on the same understanding of them Another document, this time from South Africa on low volume sealed roads (LVSR), contains a paragraph which refers to different standards and guidelines from various countries. It says that:


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Listing Highway Parameters - Part 2: Discussion "All the guidelines/manuals listed above are based on different philosophies and make different assumptions or use different criteria for developing design values for the various design elements. For example, some guides give emphasis to safety considerations while others may place emphasis on service level, capacity, comfort or aesthetic values. Not surprisingly, the resulting design values recommended, and their related cost implications, all differ,sometimes quite significantly. Thus, it is essential for the designer to have a thorough understanding of the origin, background and basis of development of the design guides or manuals and related design criteria as a basis for adaptation, where necessary, and subsequent judicious application to LVSR situations". (ref 1042, South Africa, 2003) Unfortunately it is not easy to get a “thorough understanding of the origin, background and basis of development of the design guides or manuals …. “ , or even to find the particular advice you may be in need of, since these documents often have an impenetrable layout, and where the advice on a particular parameter is fractured across different chapters and sections of the document, without any clear cross-link between them.

Working definition of a “standard” Documents on the geometric design of roads come in various shapes and formats, from textbooks to research papers, government advice notes, and in some cases even Powerpoint presentations. For the purpose of this document, a definition of a standard might be: "In the context of the geometric design of roads, a standard is a document with some claim to authority, which provides information and guidance on the geometric design of roads" Author


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Listing Highway Parameters - Part 2: Discussion 2.2.2 Identifying relevant standards “Standards” - useful documents which describe the geometric design of roads - are published in many different countries and many different languages. After all there is no reason to suppose that (for example) a document published in Germany or China, or in the French or Russian languages, is not as useful as s document which is published in the UK, or in English. A first step towards identifying these standards was made with the publication of the document "Road design standards - by country", which is also a “Global Transport Atlas” document. The latest version 6.1.1 was published in September 2016, and covers 79 countries and includes details of 7 multi-country standards. The purpose of the document is stated as: "Most countries issue their own guidelines on highway geometric design (and some issue more than one guideline). The guidelines offer a good place to start from when a new project involves road design in their country. Compiling a document on guidelines in different countries is also one step towards identifying current best practice in design. . This document provides an overview of what the current standards are in a number of different countries. The details are as accurate as could be prepared at the time of publication, but there are no claims that they are either complete or fully up to date”. The publication is associated with a digital document archive of standards which presently contains over 2,000 publications from a number of countries, and in a number of different languages. Other sources of information on standards include online lists of publications. For example, some technical organisations have searchable databases with details of their technical publications and standards.


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Listing Highway Parameters - Part 2: Discussion 2.2.3 Extracting relevant parameters Some standards make it easy to identify at least some relevant parameters, whilst others seem to make it particularly difficult, even without a consideration of terminology (see later). Examples of the former include a document issued by the City of Norwalk, USA on “basic design controls” (ref. 2388) and Delaware Department of Transport’s Road Design Manual (ref. 1010), which has a separate chapter on “Design controls”. Here, “design control” could be seen as alternative term for “parameter”. Less easy documents include standards where the use of terms to refer to a particular parameter is not consistent, where these terms / parameters are not defined, or where the discussion of a parameter is fragmented into parts spread across a hundred pages or more of text . Further, some parameters fall out of fashion, as did a number of parameters for the measurement of length (e.g. ell, rod and perch). Other, new parameters may appear -for example “curvature change rate of the single curve“, as in:

"The case of two-lane rural roads with traffic volumes in the range of 1 000 to 12 000 vehicles per day as reflected in United States, German and Greek databases was considered in order to assess the impact of various design parameters, e.g. lane width, radius, sight distance and gradient, on the variability of operating speeds and accident rates4. It was found that most of this variability could be explained by a new parameter, Curvature Change Rate of the single curve (CCRs)". Ref.929, Germany / South Africa, 2001 This means that trying to prepare a list of parameters in geometric road design is not as straight-forward as might be expected. There is also the problem of terms, the combination of words used to name a particular parameter (see next section).

Approach used for this document

This involved a search through a large number of (mostly digital) documents. The main steps are: ● ● ● ● ●

Restrict the initial search to a single language (English) Find relevant standards Extract parameters Find one or more definitions for each parameter List parameters together with a source reference and one or more definitions


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Listing Highway Parameters - Part 2: Discussion 2.2.4 A note on terms and language A note on terms Any discussion on geometric road design cannot avoid some consideration of technical terms and the language they are expressed in. Here, “terms” are the groups of words which become the “names” of different geometric design parameters. The present version of this document mainly refers to design standards which are published in just one language (English). But this does not mean that these standards use the same term for a particular parameter - or indeed that they use the same term consistently within their own document. Even where two standards use the same term for a geometric parameter it would be wrong to assume that they have the same definition for the parameter. This makes it risky to use advice from a standard which does not have any definitions at all. We can find examples where different terms refer to the same parameter, and where the same term can have different meanings. This may also cause problems, as where a writer of one standard uses material on a geometric parameter from a number of other standards, and where these other standards have different definitions for the parameter. It is not unusual for one standard to take material from a number of other standards. In a perfect world this might be acceptable. But where two or more different definitions can be found for the same parameter, design engineers should take this as a warning sign. To take a basic example we can find several different definitions - and suggested dimensions for a parameter as basic as a design car. If the engineer from country A uses a standard from country B to design a car park, perhaps the resulting parking spaces will be too small for the local vehicle fleet. The following table gives some examples. This document has its own section on “definitions”, but it might be useful to include two of them at this point: Definitions Either an explanation of the meaning of a parameter, found in a standard or, where an explanation cannot be found, one or more examples of the use of the term. Standards A collection of documents, including all the national and local standards identified in the publication "global standards", and also a large number of technical papers and reports which cover topics in the road design area. A note on language Where the tems for parameters are in English there may be several alternative terms for the same parameter. The same is probably true for other languages. The result can make a complicated situation almost impossible, once a language translator has been at work. Take for example the parameter "harmonic mean speed". In English there are three alternative terms which represent this parameter, and perhaps standards published in Spanish also have three different terms for it. Translators would then have to work with nine different possible combinations of terms - without even considering that many translators who are not also technical specialists will probably come up with new terms of their own.


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Listing Highway Parameters - Part 2: Discussion Table 1: Problems associated with terminology

Problems Different words, same meaning

Example ● ● ●

Notes

macroscopic mean speed space mean speed harmonic mean speed

Source

A distinction is drawn between Ref. 2247 microscopic mean speed and macroscopic mean speed. The former is the average of the individual speeds of a sample of vehicles and is also referred to as ‘time mean speed’. The latter, also referred to as ‘space mean speed’ or ‘harmonic mean speed’, refers to the average travel times across the length of the roadway.

Same words, different meaning

Flat terrain

For example, ● Flat terrain with largely Ref. 294 unrestricted horizontal and vertical alignment; transverse terrain slope between 0 and 10 percent And ● The topographical condition Ref. 763 where highway sight distances, as governed by both horizontal and vertical restrictions are generally long or could be made to be so without construction difficulty or expertise. The natural ground, cross slopes (i.e. perpendicular to natural ground contours) in a flat terrain are generally below 3%

Same words, meaning changes with road type

Profile grade line

For highways, superelevation is usually applied by rotating the cross section about the profile grade line. This will be the centerline in the case of two-lane highways, undivided multilane highways, and multilane divided highways with paved medians.

Ref. 782

For multilane divided highways with wide medians, the inside edge of traveled way is often used as the axis of rotation. For freeway ramps, the axis of rotation will normally be the edge of traveled way closer to the freeway; however, it may be shifted to avoid sags in the edge grade of the ramp.


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2.4

Listing parameters

Introduces the idea of associating parameters with levels of importance. Discusses the development of a structured list of parameters.

2.3.1 Parameters and levels of importance Parameter groups Section 1.2 above explained that there are hundreds of parameters in the geometric design of roads, and introduced the idea of “parameter groups”, where the parameters in each group have a common theme. For a particular group, the resulting list of parameters might then give the impression that all geometric parameters are equally important - but of course, this is not the case. A quick search through a number of standards will produces terms such as key parameters, important parameters and critical parameters, as for example: “.... In describing traffic streams in quantitative terms, the purpose is to both understand the inherent variability in their characteristics and to define normal ranges of behavior. To do so, key parameters must be defined and measured”. Ref. 1036, USA, 2004 And “The Manual deals with each of these road types and the national standards for particular road types are set out and explained in Part B. Part B can be used by the engineer or others who simply needs to look-up the values of the key parameters”. Ref. 1005, Ethiopia, 2011 “Design speed is a most important parameter in road design. It is used to select geometric design features such as alignment and cross section elements”. Ref. 1888, Australia, 2006 “The curvature of crest curves should be sufficiently large in order to provide adequate sight distance for the driver. In order to provide this sight distance, the curve length L is a critical parameter”. Ref. 587, Ireland, 2003

There are at least two ways to identify the level of importance of a particular parameter. One is to note that some parameters are dependent on others. For example, horizontal radius is dependent on parameters such as "design speed" and "superelevation". A second way of identifying levels of important that some parameters are related to others, but imply more detail. For example,


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Listing Highway Parameters - Part 2: Discussion ●

Parameters such as "port roads" and "forest roads" are more detailed types of the parameter "resource access road"

●

A design parameter such as "control lines" might be related to a more detailed level such as "axis of rotation", and this in term to yet another level, such as "rotation about the centerline profile of traveled way"

2.3.2 Giving parameters a structure Other publications refer, at least indirectly, to the concept of a structured list of parameters. For example the document “Road engineering for development, 2nd ed.” (ref.856) includes the following graphic from a publication by Beaumont and Beavan:

Here the list steps down as in ●

Engineering/Economics ○ User co sts ■ Topography


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Listing Highway Parameters - Part 2: Discussion The list of parameters in part 4 below combines the ideas of “parameter groups” and “levels of detail” to produce a list of parameters sorted into one of a number of levels. The list from reference 856 above would appear as:

Parameter group

Parameters Level 1

Level 2

Level 3

Economics User costs topography

And, examples of other parameters: Parameter group

1. Road type

Parameters Level 1

Level 2

Resource access road

Port roads

Level 3

Forest roads

2.Vehicles

Non-motorised transport

Bikes

Conventional bike Bike with child trailer


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Listing Highway Parameters - Part 3: Notes on the Parameters

PART 3 - NOTES ON THE PARAMETERS

Notes on the parameters grouped as follows:

1. 2. 3.

Road type Vehicle type Road users


4.

Geometrics 4.1. Speed 4.2. Controls 4.3. Horizontal alignment 4.4. Vertical alignment 4.5. Cross-sections 4.6. Parking 4.7. Junctions

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5. 6. 7. 8. 9.

Geography Economics Engineering Aesthetics Concepts

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1

Road types

Level 1 parameters

Road types is a group of parameters which refer to the intended use of the road, and sometimes to the road's function or design.

● ● ● ● ● ● ● ● ● ● ● ● ●

Resource access roads Low traffic roads Low speed roads Speed range roads Land use roads Special function roads Vehicle type roads Other roads Special section roads Weather roads Transport function roads Junction links Streets

Discussion The initial search through the available standards looked for words such as "road, street, freeway, expressway". It produced a starter list with over a hundred terms. Some standards not only list parameters of this type, they also give the list a structure. So for example, one standard gives a structured list of 28 different types of street (ref. 2328, Australia, 2016). The initial search also identified a number of problems, for example on topics such as: ● Functional classification ● Inconsistent technical terms ● Related terms

Functional classification Road classification is a subject which is worth a full discussion of its own; functional classification is only one example of it - indeed, the technical literature includes more than 80 different ways of classifying roads. But functional classes are not necessarily the same as road types. One reason is that function depends on scale - for example, what might be an important, arterial road on a city scale might only be an access road on a national scale. It can even be argued that functional classification simplifies to just three classes, regardless of the scale being considered: ● Short distance traffic roads ● Intermediate distance traffic roads ● Long distance traffic roads This idea of just three classes of function can be seen in a the text of a number of technical documents. For example a UK reference (ref. 2352) on industrial estate roads suggests three classes (approach roads, access roads and culs-de-sac). Another document, the AASHTO Green Book (ref. 831) says that “the principal arterial system is stratified into the following three classifications: (1) Interstate highways, (2) other freeways and expressways, and (3) other principal arterials”.


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Listing Highway Parameters - Part 3: Notes on the Parameters Arguably, a functional classification will say what a particular road is for (e.g. long-distance traffic) but not how important a road is, and certainly not whether a road has a particular design speed, or number of carriageways, lane width, maximum gradient and so on. Inconsistent technical terms Even with standards published in the same language, the use of terms to describe a particular parameter can be loose, with the meaning of the term / parameter changing depending on who is describing it. One such term is “Expressway”. Here are some descriptions of the term: Expressways are functionally classified as Other Principal Arterials and are constructed with partial control of access. (ref. 2327, USA, 2016) Freeways. The highest type of arterial highway is the freeway, which is defined as an expressway with full control of access (ref. Xxxx, USA, --) Expressway. A divided arterial highway for through traffic with full or partial control of access and generally with grade separations at major intersections (ref. 2396, USA, --) Expressway - An arterial highway with at least partial control of access, which may or may not be divided or have grade separations at intersection (ref. 1623, USA, 2012) It seems that, even when referring to documents from just one country and one language,, an expressway may or may not be divided, may or may not have full control of access, and may or may not have grade-separations. This inconsistency suggests that the term “expressway” cannot be taken as a specific road type parameter. Related terms (1) Rural roads, urban roads Some design standards distinguish between urban and rural areas, and between urban and rural roads. But often the meaning of “rural road” can be very vague in the sense of implying specific geometric values - the term could refer to a road with a design speed of 40 km/hr as easily as one with a speed of 120 km/hr. Further, road geometric standards do not agree that land use / topography can be split simply into only two types. For example, although the AASHTO Green Book (Ref. 831) explains the need to distinguish between urban and rural areas as in: “Urban and rural areas have fundamentally different characteristics with regard to density and types of land use, density of street and highway networks, nature of travel patterns, and the way in which these elements are related”. (ref. 831, USA, 2011) .... other documents add further types of area. For example the Illinois BDE document (ref. 2327) introduces three types of land-use area, adding “suburban” to the list, and a document from South Africa (ref. 148) introduces yet another term (“metropolitan areas”),. Keith Wolhuter (ref. 2247) goes even further, and introduces eight types of “sub-area”. Here is a quote from his publication: “As discussed later, design of roads in urban areas differs completely from that in rural areas. Urban areas include a wide range of vehicle types moving in high volumes and relatively low speeds, whereas in rural areas the differences in vehicle types becomes less


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Listing Highway Parameters - Part 3: Notes on the Parameters critical, speeds tend to be high and volumes low. Within these two areas, many subareas also present themselves such as. ● ● ● ● ● ● ● ●

Urban centres Urban corridors Suburban corridors and nodes Industrial corridors Residential areas Rural town centres Transitional areas Rural connecting corridors

There are significant differences between these subareas in the types and numbers of vehicles present. Traffic patterns and speeds differ and the needs of the people in each are also going to differ” (ref. 2247, CRC Press, 2015) In this case, the values for design parameters of roads in these areas would probably be different. We could then have road type parameters such as urban centre roads, transitional area roads and so on. In the present document, the two terms rural road, urban road still appear in the list of parameters, but with some reservations. Related terms (2) High speed roads, low-speed roads There is a similar inconsistency in the use of these terms. For example one source (ref. 2327) refers to high speed roads as “high-speed facilities (i.e., posted speeds of 45 mph (~ 70 km/hr) or greater)" - but other sources refer to different values of speed and different parameters of speed: A maximum rate of 0.06 (of superelevation) is recommended for urban high-speed roadways (50 mi/h or greater) (Ref. 829, USA, 2004) "High speed rural roads - These are roads that are designed for operating speeds in excess of 90 km/h. This may include freeways, which are intended to provide a high quality of service for large traffic volumes". (ref. 1887, Australia, 2010) "High speed roads - On high standard roads, ie. where design speeds are 100 km/h or higher, drivers tend to adopt a relatively uniform travel speed. This will generally be less than the speed assumed for the design of individual geometric elements but drivers will expect to be able to maintain a high travel speed on this type of road". (Ref. 80, New Zealand, 2003) Another source (ref. 1887) refers to intermediate speed roads, which makes a simple two-way split into high speed/low speed roads somewhat less defensible.


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Listing Highway Parameters - Part 3: Notes on the Parameters Detailing "road type" parameters

The details of these parameters are contained in a series of documents as described in section 1.3 above: General documents Table of parameters

A structured list of parameters


A document with one or more definitions for each parameter.

List of references

A list of source documents, with details such as country of publication

And Specific documents List of solutions

List of different solutions such as (here) “special function road / S2 / industrial estate road - access road”, with notes

Solutions

Documents with standard layout for this parameter group, each with detailed information on one particular solution..

Further reading ●

GTA 304 - A list of road classifications


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2

Vehicle types

Level 1 parameters

Vehicle types is a group of parameters which refer to the objects which use the road as a transport route. They include trucks and cars, pedestrians and cyclists, and wheelchair users and skateboarders.

● ● ●

Motorised transport MT Non-motorised transport NMT Dimensions

Discussion “Vehicles” include trucks and cars, pedestrians and cyclists, and wheelchair users and skateboarders. As with "road type" parameters, some standards not only list a number of vehicle types, they also give the list a structure. On vehicle types, the 2011 edition of the USA’s AASHTO Green Book says: “Key controls in geometric highway design are the physical characteristics and the proportions of vehicles of various sizes using the highway. Therefore, it is appropriate to examine all vehicle types, establish general class groupings, and select vehicles of representative sizes within each class for design use”. (own emphasis) (Ref. 831, USA, 2011) Here we have the idea of vehicle type class groups, each group containing a number of different vehicle sub-types. We can use details from this reference to begin to create a structured list of vehicle types. The AASHTO Green Book has the types : cars, buses, trucks - and adds a fourth vehicle type (recreational vehicles). It also suggests four sub-types for “buses”. This gives a structured list such as:


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●

Motorised vehicles ○ Public motorised transport ■ Bus ● Articulated bus ● Inter-city bus ● School bus ○ Conventional school bus ○ Large school bus

Table 2-1b in the AASHTO Green Book has 4 vehicle types and 19 sub-types. But other standards, from the USA and from other countries produce different lists of vehicle types. This creates a number of potential problems for road designers, including the following: Same country, different vehicle types It might be thought that, once a respected organisation in a country suggests a particular set of vehicle types and design vehicles, then this set would be used all over the country. This isn’t necessarily the case. To continue to use the USA as an example, ●

California DOT’s Highway Design Manual 2012 (ref. 1919) refers to a STAA Design Vehicle which does not appear in the AASHTO guide; and

●

the “Los Angeles 2010 bicycle plan, technical design handbook” (ref.917) gives details for four different “bicycle“ design vehicles which don’t appear in the AASHTO book

Same vehicle types, different countries Some countries decide to use vehicle type details from the design standard of another country. The Tanzania road standard apparently takes its dimensions for bicycles from a standard from Norway. But on Tanzania's roads there are types of bicycle which would be unusual for Norway (for example, gupa work bikes) - so the dimension details from Norwegian practice don’t really fit. The same could well be true if engineers in Pakistan were to use the AASHTO truck vehicle types as design vehicles for their roads. Non- “western” vehicle types The AASHTO set of design vehicles might be described as a “Western” set. The set could well be suitable for countries with a similar history and similar use of vehicles, but it may not be suitable for other parts of the world. Examples of “non-western” vehicle types include Tanzania (gupa work bikes), Peru (motocarros), Nepal (bullock carts), and Bangladesh (work rickshaws). Vehicle type relates directly to design vehicles – the traffic which the road is to be designed for. The choice of vehicle types for a road affect such parameters as lane widths, cross-section and design speed(s). On this point a presentation by Dr. John Rolt of the UK’s TRL (ref. 2211) has some relevant comments. For example, Dr. Rolt says: "In countries of South East Asia, the traffic on rural and semi-urban roads comprises many motor cycles, motor cycle taxis, pedal bicycles and pedestrians. You may be surprised to know that a typical rural road in a country like Cambodia may carry 2000 motorcycles, 1000 pedal bicycles, 1000 pedestrians but only 5-10 cars or other 4-wheeled plus motorised vehicles". And


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"It is fairly obvious that geometric standards should not be the same as in countries where motorcycle and pedal cycle traffic is almost non-existent".

Motorised transport (MT) The second-level parameters here are presently: ● private motorised transport ● public motorised transport ● commercial motorised transport ● other motorised vehicles ● other categorisations

Non-motorised transport (NMT) The 19 vehicle types in the AASHTO table referred to above are all motorised vehicles. But there are many other forms of transport, on every country’s roads, which do not have engines. One standard says that designing for all road users: ● ●

includes non-motorised vehicles, pedestrians, etc. has implications for almost all aspects of road design, including carriageway width, shoulder design, side slopes and side drains (ref. 1042, multi-country, 2003)

The second-level parameters for NMT are presently:: ● Bicycles ● Pedestrians ● Other human-powered transport ● Animal transport Bicycles and Pedestrians are perhaps obvious sub-sets. But, even in the 21st century, Animal Transport is still also a recognised mode of transport in many countries. In the online publication, the “Agri Handbook for South Africa” (link) (http://www.agribook.co.za/), Craig Macaskill writes: “Animal Power is still used on a large scale in many third world countries throughout the world and is beginning to make a comeback in many first world countries as well. In the United States of America, Animal Traction is used in particular by the Amish people as a major power source for their agriculture and transport. In the United Kingdom, Europe and Canada Animal Traction is used more as a hobby but some areas have seen an increase in the use of animal traction, notably in the forestry industry and for cartage over short distances e.g. on-farm, milk delivery and fertiliser application.” On Other human powered transport, one World Bank publication (re. 919) says that the vast majority of trips on the rural transport network infrastructure in developing countries are made made by non-motorized means, including walking, animals, bicycle, and porterage. Paul Starkey, in his 2013 paper for the World Bank (ref. 2359) says that “In sub-Saharan Africa, most village transport still involves people (mainly women) walking and head loading”, whilst his table 1 includes wheelbarrows and hand carts as distinct means of transport”. (ref. 2359, multi-country, 2000)


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Vehicle dimensions Road design standards often include details of their suggested design vehicles. However these dimensions usually are only for the vehicle “as built”, and often often exclude objects such as car wing mirrors. The dimensions of a vehicle can change depending on the way their owners use them. For example, the height of a car in use might increase with the addition of a luggage rack, the length increase with the addition of a rear cycle rack, and the width increase if we include wing mirrors. Different values for (for example) vehicle length change according to different types of dimension, such as: ● basic dimensions ● in-use dimensions ● effective dimensions ● inter-vehicle dimensions ● turning path dimensions ● other dimensions

In use, cars may carry bicycles or luggage roof racks and other luggage on the roof, or on fittings at the rear of the vehicle;

.... and the operating envelope for a parked car in a supermarket car park will need more space than that indicated by the as-built vehicle dimensions.


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Listing Highway Parameters - Part 3: Notes on the Parameters Basic dimensions Road design standards often provide details of the dimensions of their suggested set of design vehicles. In-use dimensions Basic dimensions often exclude objects such as car wing mirrors. Here for example: “The legal width of commercial vehicles is 2.5 m. The majority of heavy vehicles are built to the maximum width, but it does not include the additional 0.2 m width on each side of the vehicle generated by wing mirrors” (Ref. 1887, Australia, 2010) Effective dimensions Vehicle dimensions can also change within seconds; for example , a bicycle with rider may only be 600mm wide, but when in motion - with the rider's knees and elbows sticking out, with the occasional wobble and uncertain linear path (bicycle riders do not necessarily travel in a straight line), more width is needed. To quote (ref. 1887) again: “Not all bicycle riders can steer a straight line and when riding uphill experienced riders work the bicycle from side to side whilst the inexperienced may wobble. Bicycle riders also need adequate clearances to fixed objects and to passing vehicles in addition to the 1 m envelope” (Ref. 1887, Australia, 2010) And to take an example of a motorised vehicle: "The effective width of trucks increases on curves (vehicle swept path considerations)" (Ref. 857, Australia, 2003) Inter-vehicle dimensions Since vehicles rarely travel alone, the interaction between them should also be included as a design parameter. Measures could include lateral inter-vehicle gap and longitudinal inter-vehicle gap. The latter is usually related to design speed (the higher the speed, the more longitudinal distance between vehicles is needed) - but rarely if ever related to vehicle type. In Germany, lateral clearances between vehicles are discussed in detail, and in terms of a vehicle envelope (Lichter Raum) and a clearance envelope (Verkehrsraum). Turning path dimensions Turning path dimensions are useful in the design of at-grade intersections, and parking facilities. They are related to vehicle type, and their proper consideration can apply as much to wheelchairs and animal transport as to trucks. Other dimensions A number of other design parameters related to vehicle dimensions, such as "headlight height" (used in calculating headlight sight distance).,


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Listing Highway Parameters - Part 3: Notes on the Parameters Detailing "vehicle type" parameters





List of references



List of different solutions such as (here) “motorised transport / public transport / bus / city bus”, with notes

Solutions


Further reading ●

The dimensions of vehicles


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3

Vehicle types

Level 1 parameters

Road User types is a group of parameters which refers to the people who use of the road, rather than the vehicles. For example, a road designer may check the design is safe for cars, but the age of car drivers may also be a parameter which affects safety..

● ● ● ● ● ● ●

Driver type Cyclist type Pedestrian type Dimensions Objects Traffic flows Other

Discussion Road users - whether vehicle drivers, pedestrians, cyclists etc - have their own characteristics which are relevant to road design - eye height, walking speed and so on. We can find reference to many types of road user in design standards. For example, one classification of bicyclists refers to the type of persons using the bicycle and not to the vehicle (the bicycle) itself (see ref. 2149). If we add this classification to the level 1 parameter the result is a structured list as: Road user types ●

Cyclist ○ ○ ○ ○ ○

types Recreational cyclists Commuter cyclists Sports cyclists Users of special equipment School children ■ Primary school children ■ Secondary school children

(based on ref. 2149, Australia, 2015) Drivers, cyclists, pedestrians The same person can be, at different times, a driver, a cyclist, and a pedestrian. This does not mean that the parameters which link the person to road design will be the same in all three cases. For example as a pedestrian he/she may pay much less attention to traffic conditions than as a car driver, and so have a slower response-reaction time.. Dimensions


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Listing Highway Parameters - Part 3: Notes on the Parameters The dimensions of road users relate to road user types in the same way that the dimensions of vehicles relates to vehicle types. For example, parameters such as driver comfort and driver discomfort can affect the design of vertical and horizontal curves. But it can be a mistake to think only in terms of drivers (and often, only in terms of car drivers). To take the example of eye height, various standards can be found which discuss design relative to the eye height of truck drivers, cyclists, equestrian riders or people in wheelchairs. Objects Objects - which might be described as passive users - and their dimensions can influence a number of design parameters. For example, AASHTO’s 2011 Green Book says: “Sight distance is the distance along a roadway throughout which an object of specified height is continuously visible to the driver. This distance is dependent on the height of the driver’s eye above the road surface, the specified object height above the road surface, and the height and lateral position of sight obstructions within the driver’s line of sight” (ref. 831, USA, 2011) The same source explains how different values for object height are used in various parameters for sight distance, vertical curves and so on. Another source refers to different types of object, still in the context of object height:

(ref. 148, South Africa, 2002: Geometric design guidelines, published by CSIR) Traffic flows Traffic flows are a separate group of parameters which affect geometric design. For example. (ref 148) says: “Factual information on expected traffic volumes is an essential input to design. This indicates the need for improvements and directly affects the geometric features and design” (ref. 148, South Africa, 2002) And, from the same reference: “Traffic flows vary both seasonally and during the day. The designer should be familiar with the extent of these fluctuations to enable him or her to assess the flow patterns. The


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Listing Highway Parameters - Part 3: Notes on the Parameters directional distribution of the traffic and the manner in which its composition varies are also important parameters. A thorough understanding of the manner in which all of these behave is a basic requirement of any realistic design” Since flows are the result of decisions by different types of road users, they are presently included in this parameter group.

Detailing "road user type" parameters





List of references



List of different solutions such as (here) “pedestrian / disabled person / wheelchair user/ wheelchair user with companion”, with notes

Solutions



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4

Geometrics

Geometrics - sub-groups

This group concerns parameters which immediately affect particular aspects of geometric design. It is divided into a number of sub-groups.


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1. 2. 3. 4. 5. 6.

Speed Controls Horizontal alignment Vertical alignment Cross-sections Parking 7. Junctions

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4.1

Speed

Level 1 parameters

These are parameters which refer to a measure of speed. Some refer to design speed, others to less obvious concepts of speed, such as base free flow speed or closing speed.

● ● ● ●

Design speed Percentile speeds Speed ranges Other speed parameters

Discussion There is a inconsistency and vagueness between many standards when it comes to measures of speed, even if we only look at documents published in English. An indication that engineers do not really understand what they mean by speed could be taken from a statement from a document published by the USA’s TRB: “Desirably there would be strong relationships between design speed, operating speed, and posted speed limit and these relationships could be used to design and build roads that would produce the speed desired for a facility. While a relationship between operating speed and posted speed limit can be defined, a relationship of design speed to either operating speed or posted speed cannot be defined with the same level of confidence”. (Ref. 1573, USA, 2002)

Design speed We might think that at least, engineers have a common definition of "design speed"; but then we find for example: "Various studies have shown that the 85th percentile speed generally exceeds the posted speed limit by a margin of at least 10 km/hr when weather and traffic conditions are favourable. For this reason, design speed is typically equated to the 85th percentile speed“ (ref. 148, South Africa, 2002) Whilst on the other hand Keith Wolhuter says simply that: “In short, design speed is the speed selected for design! “ (Ref. 2247, CRC Press, 2015)


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Even if there were agreement on a definition of "design speed", its values can vary with the type of vehicle - so that a road design based on a design speed for cars has to be stress tested for design speeds (etc.) for trucks, cyclists and the other vehicle types which will use the road. Design speed can also vary with the weather (wet road design speeds), type of terrain, type of road, and road function. Even the concept of design speed as a useful tool is itself in doubt, with discussions looking at ideas such as “context sensitive roads”. Here for example (ref. 802) refers to research by Garrick and Wang (2005) which” examined context-based alternatives to the use of design speed as a controlling criterion for design of streets and highways”. Percentile speeds Several parameters of speed refer to percentile speeds, such as the 85th percentile speed. This has been referred to as the operating speed: ".... the 85th percentile speed of cars at a time when traffic volumes are low, and drivers are free to choose the speed at which they travel. In effect, this means that designs based on the 85th percentile speed will cater for the majority of drivers". (Ref. 1885, multi-country, 2010)

Speed ranges This idea is referred to in the discussion on high-speed/low speed roads in the notes on the "road types" group above. But some standards also refer to this distinction as a variant of design speed, as for example: "Road design guides contain many simplified methods to compute overtaking distance and these vary widely, especially at high design speeds" (ref. 80, New Zealand, 2003) And "High design speeds of 80 km/h [50 mph] and above are generally applicable to highways in level terrain or where environmental conditions are favorable " (ref. 831, USA, 2011) Although such terms can be found in a number of standards, there is not necessarily any agreement on what the values for the terms should be. Other speed parameters The present listing has around 80 parameters under this heading.

Speed for horizontal and vertical alignments We might expect that, for any particular design project, the design speed used in the design of horizontal and vertical alignments would be the same. However this is not necessarily the case. For example, (ref. 2380) says


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Listing Highway Parameters - Part 3: Notes on the Parameters “The design speed of the road in both the horizontal and vertical planes should generally be the same. A reduction in the vertical design speed (compared to the proposed horizontal design speed) should only be considered when; ● ● ●

the terrain is such that significant cost reductions may be achieved, and a risk assessment has been undertaken to determine the safety impacts of any reduction in vertical design standards and measures taken to address the significant risks and provide for the safe operation of the road.” (Ref. 2380, Australia, 2016? )

Further reading ●

Notes on design speed, blog post dated 7th October 2016


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4.2

Control elements

Level 1 parameters

These are parameters wwhich control or restrict the geometric design of a road. For example, a basic e calculation of minimum horizontal curve radius might give a figure of 500 metres, but the designer may add a factor of safety which gives a figure of 750 meters.

● ● ● ●

Factors of safety Control lines Control checks Other

Discussion The idea of design controls is not new. For example the Delaware DOT's Road Design Manual (ref. 1010) has a full chapter on the topic. The document also refers to different types of control, including: • Speed related controls • Traffic related controls • Other design controls ○ Terrain characteristics ○ Functional classification ○ Access control ○ Economics ○ Safety ○ Environment The Austroads document on "Design considerations" (ref. 1888) refers to alignment and grade line controls, and to cross-section controls. Another Australian document (ref. 585) says that "Before setting out a proposed alignment, it is necessary to identify any controls on its position" (and goes on to refer to two types of control, mandatory and discretional). It suggests such alignment controls include • Operating speed • Environmentally sensitive areas • Costs • Terrain Many of these "controls" are what are referred to in the present document as parameters, and so perhaps an "operating speed" control would be a specified minimum value for operating speed of vehicles on the completed road.


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There is a inconsistency and vagueness between many standards when it comes to measures of speed, even if we only look at documents published in English. An indication that engineers do not really understand what they mean by speed could be taken from a statement from a document published by the USA’s TRB: “Desirably there would be strong relationships between design speed, operating speed, and posted speed limit and these relationships could be used to design and build roads that would produce the speed desired for a facility. While a relationship between operating speed and posted speed limit can be defined, a relationship of design speed to either operating speed or posted speed cannot be defined with the same level of confidence”. (Ref. 1573, USA, 2002)

Factor of safety This is where the design engineer believes he can control the safety of his design (and allow for uncertainties and possible over-simplifications in the design theory) by modifying the theoretical value of a parameter to make it more safe. To give some examples: a document from Ethiopia, after discussing the problems of identifying representative values for longitudinal and side friction in the country, says: “The values used in this manual (....) allow a reasonable safety factor to cater for the wide range of conditions. For unpaved roads a systematic reduction in the values used for paved roads has been used.” (ref. 1978, Ethiopia, 2013) And “The values of side friction factor f for use in geometric design are shown in Table 7.4. It is important to note that the absolute maximum values for f given in Table 7.4 assume construction and maintenance techniques that will ensure an adequate factor of safety against skidding”. (ref. 1887, Australia, 2010) And "It is inappropriate for designers to ‘experiment’ with driver perception-reaction times (t), but they can use lower figures supported by credible rationale for risk assessment in diffficult situations. MfS uses 1.5s, this being based on test values with a 67% increase as a factor of safety. It is over twice the value used for Highway Code distances, but the point is made that the Code reflects emergency stopping scenarios". (ref. 2381, UK, 2008) Unlike this last reference, standards usually do not state what values they use for a factor of safety, and often do not even say when or where they use them. This presents a problem for the designer. As another standard says: “It is essential for the designer to have a thorough understanding of the underlying criteria and assumptions that have influenced the development of existing design guides or manuals


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Listing Highway Parameters - Part 3: Notes on the Parameters as a basis for adapting them, where necessary, , to suit the local road environment. (ref. 1042, multi-country, 2003)

Control lines A control line is an imaginary line along a design for a new road. For example, (Ref. 2133) says that “The horizontal and vertical elements of a road are described in terms of control lines. Control lines are lines mathematically defined in the horizontal and vertical planes”. (ref. 2133, Canada, --) There are different types of control line, as for example: ● Vertical alignment control line ● Horizontal alignment control line ● Superelevation axis of rotation Further, the suggested location of control lines can change with different standards and with the type of control line; individual standards may even allow different locations of control lines within one project. In this document, each type of control line is considered to be a separate design parameter. Control checks A search through available standards has produced a number of specific control checks. For example: "Check sag vertical curves through underpasses to ensure that the underpass structure does not obstruct the driver’s visibility. Use the following equation to check sag vertical curves through underpasses .... " (ref. 2327, USA, 2016) Other checks These parameters represent a number of checks covered by a single procedure. Examples are ● ●

Checklists - A list of things, names, etc., to be checked off or referred to for verifying, comparing, ordering, etc (Ref.2327, USA, 2016) Design briefs, as in: The client and the design team should establish the design brief jointly. The purpose of the design brief is to establish the technical aspects and constraints affecting the design.

Further reading ●

Road geometric design – control lines blog post dated 10. October 2015


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4.3

Horizontal alignment

These are parameters which strongly influence the design of the horizontal alignment of a road. Some, such as parameters related to friction, also influence the design of the vertical alignment.

Level 1 parameters ● ● ● ● ● ● ● ● ● ● ● ●

Acceleration Deceleration Straights Circular curves Transition curves Other curves Friction Sight distance Sight distance types Crossfall Superelevation 3D design

Discussion Parameters in this group occasionally give examples of uncertain practice. Discussed in some detail under "acceleration", there are likely to be examples in parameters in the other sub-groups as well. Acceleration and deceleration There are a number of potential problems with these parameters. For example , there are different types of acceleration (centrifugal, centripetal, vertical etc); and acceleration (and deceleration) may vary with parameters such as ● Weather ● Type of road surface ● Type of vehicle ● Type of road section (e.g. mountainous, in tunnel) ● Level of comfort ● Design speed (ref. 856 has a table giving minimum levels of acceptable vertical acceleration for different design speeds) Table 5.3 in (ref. 1887, Australia, 2010) lists different values for the coefficient of deceleration with reference to these conditions.


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(excerpt from table 5.3, ref 1887, multi-country, 2010) If there were 3 different values for the 6 conditions in the bullet list above then engineers might have some 700 values for deceleration to choose from. Few standards relate values of acceleration or deceleration to all these different conditions. Where a standard does give a specific value, the value may be out of date, for example: "British design practice is based on the fundamental assumption that at absolute minimum radius the 99th percentile vehicle should not experience more than the maximum level of centrifugal acceleration acceptable for comfort and safety, This was established at about 0.22 g some 70 years ago and has not been changed since". (1038, --, 2006) Where the value is not out of date, it may include a hidden factor of safety.

Straights, curves and transitions As (ref. 856) puts it, the horizontal alignment of a road ".... consists of a series of intersecting tangents and circular curves, with or without transition curves". Tangents are also known as straights, and transition curves can have one of a number of forms (parabolic, clothoid, several step compound arc, etc.). The parameters of curves are related to a measure of speed such as design speed, and design speed itself is related to other parameters such as vehicle type.

Sight distance The present list of these parameters has over 50 different types of sight distance parameters. Some relate a particular type of sight distance to one or more of the following: ● road surface, ● weather (wet or dry roads), ● vehicle type, ● design speed ● road gradient ● deceleration rate ● object height


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Listing Highway Parameters - Part 3: Notes on the Parameters ●

driver eye height

It seems likely that these features affect most measures of sight distance, although the standards available so far do not seem to indicate this. Crossfall and superelevation There seems to be a potential disagreement in the standards on the meaning of terms which may or may not mean the same thing, such as: • Crossfall • Cross slope • Camber 3D Design Three-dimensional design will probably lead to a holistsic approach to road geometric design. This could well be an improvement on the current approach, which is on the lines of "design horizontal alignment, design vertical alignment, check that there is no contradiction between them" 3D design may lead to some existing parameters disappearing, and new ones appearing.


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4.4

Vertical alignment

Level 1 parameters

These are parameters which strongly influence the design of the vertical alignment of a road.

● ● ●

Grade Vertical curves Vertical clearance

Discussion There is no level 1 parameter here for "3D design", since it already appears under "horizontal alignment". Grade Here too there may be some confusion of terms in different English-language standards, between for example ● ● ● ●

Gradient Grade Longitudinal slope Vertical tangent

It is likely that different standards make different uses of the same term. Vertical curves These notes contain parameters related to vettical curves Vertical clearance Different measures related to the clear space above or below a vehicle and to potential obstructions (such as the underside of a bridge).


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4.5

Cross-section parameters

These are parameters which make up the width of a road.Some refer to specific features such as traffic lanes, others to parameters which relate to width or horizontal clearance.

Level 1 parameters ● ● ● ● ● ● ● ● ● ● ● ● ●

Traffic lanes Medians Shoulders Separators Verges Edges Curbs Special use elements Horizontal clearance Right of way widths Overall widths Other General

Discussion A road cross-section can be seen as consisting of a number of modules. Adding the widths of the modules together would give a measure of the overall width of the road. The above level 1 parameters fall into one of two groups, those which represent modules, and those which represent a measure of width. A number of standards specifically discuss the features which make up a road cross.section, and so are one source of this type of parameter. Examples includes ● Transit New Zealand's "State highway geometric design manual chapter 6 - cross-sections", ● Helsinki, Finland's "KATUPOIKKILEIKKAUSTEN SUUNNITTELUOHJEET" - "Street cross-sections" (ref. 2144) and ● Ireland's "TD27 - cross-sections and headroom" (ref. 1196). A question of width It is worth mentioning that sometimes the meaning of “width” is not clear (for example, is the width of a traffic lane measured from the centres of the lane markings or the inside edges of the lane markings?). Standards contain different measures of "width", such as ● ● ● ● ● ● ● ●

Acceptable width Appropriate width Desired width Effective width Maximum width Minimum width Standard width Sufficient width


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Values given by standards for “width” may also vary with other parameters, such as the type of road, type of vehicle using it, the design speed of the road, the road element (e.g. a tunnel) and so on.

Standard cross-sections A number of standards use different ways to present details of the elements which make up a cross-section, and the widths of the elements. These imply that the figures represent in some way an approved cross-section, although it is not always clear whether the cross-sections are a required design or simply suggested as a good idea. Here are two examples:

(ref. 2144, Finland, 2001) And

(Ref. 1196, Ireland, 2011)


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4.6

Junction parameters

These are parameters which describe nodes in a road network.Some refer to types of node, others to elements which make up the node

Level 1 parameters ● ● ●

Interchange types Junction types Junction details

Discussion Once again, even in English-language standards, there is some confusion and some inconsistency in the use of terms. For example, one New Zealand document gives alternative terms for the same element (e.g. Y intersection, Y junction). For the present document, ● ● ●

A junction is any node in the road network An interchange is a grade-separated junction An intersection is an at-grade junction

One source subdivides interchanges into free-flow and standard grade-separated interchanges (ref.1956). This parameter group needs further development. Also, some parameters are / or could be included elsewhere - for example, ramp width and ramp gradient under cross-section and vertical alignment respectively.


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4.7

Parking parameters

These are parameters which relate to parking facilities.

Level 1 parameters ● ●

Parking types Parking elements

Discussion These parameters have been arranged into two groups. They are meant to cover all types of parking facility except on-street parking, which is covered in the "cross-section" sub-group. Parking types The parking types listed here refer to vehicle type, parking purpose etc. They can affect the dimensions of various parking elements- for example, the width of a parking space. The width has to be greater for trucks than for cars, and greater for shopper parking than for commuter parking, Parking elements The values which standards suggest for the dimensions of a parking element also vary with expressions such as "minimum", "maximum" and so on. Taken together with the differences suggested by parking types there should be a set of multidimensional matrices where the values for e.g. width are listed.


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5

Geography

Level 1 parameters

A group of parameters which refers to the changing physical surroundings which the road is to fitted into.

● ● ● ● ● ●

Terrain types Terrain and other parameters Development Climate Climate with other parameters Environment

Discussion Geograhy is widely recognised as having an important influence on road design. For example, Austroad's "Guide to road design - part 2, design considerations" (ref. 1888) has a checklist for design considerations has a number of points under the heading "geographical factors".

(ref.1888, multi-country, 2006) There is even a textbook on the topic, titled "The geography of transport systems" (ref.2047) Terrain, development The Delaware DOT manual (ref. 1010) has this to say on terrain and development: "The selected design speed should be logical with respect to the characteristics of the terrain, adjacent land use, and functional classification. A highway in level terrain may justify a higher design speed than one in rolling terrain. A highway in lightly developed or undeveloped (open) areas may justify a higher design speed than in a developed area " (own emphasis) (ref. 1010, USA, 2004) Whilst, the Austroads document referred to above (ref. 1888) says: “The design speed is probably the most influential factor affecting the geometric design of a LVSR and is influenced by the following factors: nature of the terrain


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Listing Highway Parameters - Part 3: Notes on the Parameters classification of the road density and character of the adjoining land use (ref. 1888, Australia, 2006)

Terrain, definitions But for both “terrain” and “development” the problem of terms and definitions appears again. Basically, even in English standards on geometric road design, the same term can mean different things in different standards - which basically means that they represent different parameters. For example, "Level Terrain Is that condition where road sight distance, as governed by both horizontal and vertical restrictions, are generally long or could be made to be so without construction difficulty or major expense". (ref. 857. ) Note that this quotation indicates economics as a separate parameter. An alternative definition for “level terrain” is: "Level (terrain). Flat or gently rolling terrain with largely unrestricted horizontal and vertical alignment; the road line crosses 0-10 five metre ground contours per kilometre" (Ref. 635, )

Development, definitions Here there are two difficulties - different definitions for the same term, and different ways of breaking down development into different, lower level parameters. Engineering design standards seem to be lagging behind the times, as there are several recent efforts at more formal definitions of (for example) urban and rural land development, as the following graphic suggests.

(ref. )


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Listing Highway Parameters - Part 3: Notes on the Parameters Climate Existing standards may only relate to road design in temperate climate. Even standards for countries subject to other climates may quote wholesale from these temperate climate standards. On this point, in "Road engineering for development, 2nd ed".(Ref. 856) Robinson and Thagesen say that: "Developing countries in the tropics often have challenging natural conditions and different institutional and financial institutions than industrialized countries. However, most textbooks on road engineering are based on experience in industrialized countries with temperate climates, or deal only with specific issues" And "Most existing textbooks on road engineering are biased towards the experience and needs of industrialized countries with temperate climates", Environment The direct effect of environment on road standards can be indicated by these quotes "The level of environmental assessment given to a project is a major consideration in establishing its design controls and standards since commitments made in these assessments must be fully incorporated in the design" (Ref. 1010, USA, 2004) And "The design standards adopted must take into account the environmental road conditions, traffic characteristics, and driver behaviour" (Ref. 635, UK, 1988)


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Detailing "geography" parameters





List of references



List of different solutions, with notes

Solutions


Further reading ● ●

Blog post on terrain classification Terrain evaluation manual / by Cliff Lawrance, Rosemary Byard and Peter Beaven


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6

Economics

Level 1 parameters

A group of parameters which refers to the financial and cost aspects of geometric road design.

● ●

Economics Economics and other parameters

Discussion Economics is another area which is recognised as having an important influence on road design. Note that for this discussion, "cost" is taken to be another term for economics. Economics may affect the overall choice of design standards. For example, one standard says: "These are roads having many curves with radii less than 150 m. Operating speeds on the curves generally vary from 50 – 70 km/h. Rural roads usually only have these characteristics when difficult terrain and costs preclude the adoption of higher standard geometry." (ref. 1887, Australia, 2010) Whilst engineers generally accept the impact of total cost on the approval of a proposed design, they may not be aware that cost can also directly influence single design parameters. For example, in a section headed "Economics", one reference says: "Decisions on alignments, grades, widths, slopes and other items can greatly influence the construction cost. Geometric and structural standards higher than needed for a particular type of facility may cause increased expenditures that might be better spent on improving additional road sections. Use of standards that are too low may be uneconomical by contributing to early obsolescence of the facility." (own emphasis) (ref. 1010, USA, 2004) And "Generally, it is impractical to design crest vertical curves that provide passing sight distance because of high cost where crest cuts are involved and the difficulty of fitting the resulting long vertical curves to the terrain, particularly for high-speed roads" (ref. 831, USA, 2011) And "The frequency and length of passing sections for highways principally depend on the topography, the design speed of highway, and the cost. "


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Listing Highway Parameters - Part 3: Notes on the Parameters (ref. 831, USA, 2011)

Detailing "economics" parameters





List of references




Solutions



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7

Engineering

Level 1 parameters

A group of parameters which refers to the financial and cost aspects of geometric road design.

● ●

Engineering Engineering and other parameters

Discussion Engineering considerations can affect the general design and in some cases a specific parameter. Perhaps an example of the former would be the statement from an Australian standard: "For construction expediency, superelevation values are normally rounded (upwards) to a multiple of 1% so that there is a corresponding adjustment of side friction". (ref. 857, Australia, 2001) An example of an engineering impact on a specific parameter could be the link between road surface and crossfall, as for example: "The normal crossfall should be 3 per cent on paved roads and 4 to 6 per cent on unpaved roads. Shoulders having the same surface as the carriageway should have the same cross slope. Unpaved shoulders on a paved road should be 2 per cent steeper than the crossfall of the carriageway. " (ref. 635, UK, 1988)





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Listing Highway Parameters - Part 3: Notes on the Parameters Glossary of parameters


List of references




Solutions



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8

Aesthetics

Level 1 parameters

A group of parameters which cover topics such as visual impact and cultural heritage.

● ●

Aesthetics Aesthetics and other parameters

Discussion Consideration of aesthetics can affect the general design and in some cases a specific parameter. A document from Australia says: “Where possible, horizontal and vertical geometry should be coordinated for appearance and safety. In principle, co-ordination means that horizontal and vertical curves should either be completely superimposed or completely separated. The related horizontal and vertical elements should be of similar lengths, with the vertical curve contained within the horizontal curve. This arrangement should produce the most pleasing, flowing three-dimensional result, which is more likely to be in harmony with the natural landform". (ref. 1887, Australia, 2010) And

"In vertical design, attempts are made to conform to the topography, wherever possible, to reduce the need for costly excavations and landfills as well as to maintain aesthetics". (ref. 1036, textbook, 2004)

Aesthetics can have an impact on individual parameters as well, for example: "The minimum rate of (vertical) curvature is determined by sight distance as well as by considerations of comfort of operation and aesthetics". (re. 771, multi-country, 2001) And "In selection of design speed, every effort should be made to attain a desired combination of safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and social or political impacts" (ref.831, USA, 2011)


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List of references




Solutions



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9

Concepts

Level 1 parameters

A group of parameters which cover topics such as visual impact and cultural heritage.

● ●

Concepts Concepts and other parameters

Discussion Consideration of “concepts” can affect the general design and in some cases a specific parameter. One problem with concepts is that, a concept which is popular today may be very much out of favour in a few years time. Since the design life of roads is often said to be 20 years, a road may be fashionably out of date before it has physically run out of life. Some concepts influence others, and some can have an impact on individual parameters as well, for example: "Smart Transportation is informed by two important concepts that have taken root in transportation and land use planning: Context Sensitive Solutions (CSS) and Smart Growth". (ref. 2415, USA, 2008) And "The concept of desired operating speed, described later in the Guidebook, is key to the context sensitive roadway" (ref. 2415, USA, 2008) The list of concepts includes a few terms taken from a list of "perspectives" in ref. 2416


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Listing Highway Parameters - Part 3: Notes on the Parameters Detailing "concepts" parameters





List of references




Solutions



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Listing Highway Parameters - Part 4 Lists of Parameters

PART 4 - LIST OF PARAMETERS

Lists of parameters are included as follows:

1. 2. 3.

Road type Vehicle type Road users


4.

Geometrics 4.1. Speed 4.2. Controls 4.3. Horizontal alignment 4.4. Vertical alignment 4.5. Cross-sections 4.6. Parking 4.7. Junctions

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5. 6. 7. 8. 9.

Geography Economics Engineering Aesthetics Concepts

Page 4-1


1. ROAD TYPES Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

resource access roads

Port roads

Level 3 parameters

Forest roads Forest tracks Haul roads farm to market roads mining and exploration road low traffic roads

LVSR - low volume sealed roads LVRR - low volume rural roads LVR - low volume roads gravel roads very low volume local roads very low volume road hill roads low traffic streets high traffic streets

low speed roads

Quiet lanes Quietways Greenways Bridleways Home zones shared space

10 km/hr zones 20 km/hr zones 30 km/hr zones

20 mph zones speed range roads

low speed roads

low speed rural road

intermediate speed roads

intermediate speed rural road

high speed roads

high speed rural roads high speed urban roadway

land use roads

Urban centre roads Urban corridor roads Suburban corridor roads Industrial corridor roads


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Residential roads Rural town centre roads Transitional area roads Rural connecting corridor roads special function roads

farm road farm to market road education road international road power tiller road telecommunications road tourism road scenic roads / routes recreational roads

primary access roads circulation roads area roads

industrial estate roads

approach road secondary distributor SDR access road

vehicle type roads

high wide load (HWL) routes emergency vehicles

Emergency access roads

buses

Busways

bicycles

Cycleways Bikeways

pedestrians

walkable urban thoroughfares off-street shared use path off-street shared use or pedestrian only path

pedestrians and functional class

Regional Pedestrian Parkways and Districts Community Pedestrian Corridors Local Pedestrian Connectors

walking trails

in general easy medium difficult handicap easy handicap difficult

trucks other roads

truck only roads

culs-de-sac shared use paths


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special section roads

Roads in tunnel Roads on bridges emergency landing strip sections underpasses 2+1 roads

weather roads

climate resilient roads winter roads

transport function road

rural road

arterial road major arterial minor arterial rural arterial Collector roads Local roads and streets other rural service / frontage road


urban road

arterial road major arterial minor arterial urban arterial Collector roads Local roads and streets other urban service / frontage road urban all-purpose road


Suburban roads

open suburban road

Metropolitan roads

1b Primary Freeways in metropolitan areas 2b Primary Metropolitan Arterial

junction links

connector road

interchange links

connector road

link roads

connector road

slip roads

connector road

loops

Interchange ramps loop ramps outer connector ramps semi-directional ramps


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directional ramps directional roadways weaving length two-lane directional roadway controlled terminals connector road

rural motorway connector road

turning roadway motorway slip road streets

Boulevards

ceremonial boulevards gateway boulevards transit boulevards

Terraces

village terraces city terraces

Retail streets

high activity retail streets local activity retail streets

Streets

city streets local streets village streets

Squares

park lands boulevards

park lands

park lands avenues park lands roads

small streets and laneways

small streets and laneways shared small street service lanes pedestrian zones

urban local streets

local urban street alleys cul de sac driveway Residential streets

local streets

neighbourhood connector A neighbourhood connector B access street A access street B access street C access street D

End of table


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2. VEHICLE TYPES Note that this table only shows the first three levels of paramaters. Level 1 parameters MT motorised transport

Level 2 parameters

Level 3 parameters

private motorised transport

car recreational vehicles

public motorised transport

bus coaches trams taxis Public service vehicles

Commercial motorised transport

2W tractor towed trailers - standard

(trucks)

4W tractor towed trailers - standard B-doubles design prime mover and semi-trailer five-axle vehicles high productivity freight vehicles (HPFV) light truck up to 2.5 tonnes gross multi-vehicle combinations PBS vehicles (performance based standards) rice truck semi-trailer WB-15 single unit + trailer SU+T single unit SU single-unit trucks single-unit trucks truck tractor-trailer combinations truck tractors with semi-trailers truck up to 10 tonnes gross truck up to 15 tonnes gross Turnpike-Double Combination (WB-33D [WB-109D]) design vehicle Type 1 road train Type 2 road train

other motorised vehicles

motorcycle scooter motocarros (Peru) taxi rickshaws auto rickshaw power tillers


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power tiller trailer tuk-tuk Jambo farm tractor other categorisations Non-motorised transport NMT bikes

Lao LVRR categories mono-cycles scooters conventional bikes tagalong trikes tadpole trikes recumbent tadpoles rickshaws cycle rickshaw cycle rickshaw cycle rickshaw

Pedestrians

adults children physically impaired (disabled) / handicapped wheelchairs groups roller skaters roller-blading inline skaters skateboarders

Other human powered transport

wheelbarrows sledge trolleys hand cart human drawn cart head porterage porters

animal transport

horse-riding mule transport pack animals and mules animal drawn cart

dimensions

basic dimensions

length width height

in-use dimensions


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length

Page 4-7


width height effective dimensions

effective width

inter-vehicle dimensions

inter-vehicle lateral gap inter-vehicle longitudinal gap (gap) vehicle envelope clearance envelope movement width safety width

turning path dimensions

minimum turning radius minimum design turning radius centre-line turning radius minimum inside radius curb to curb turning radius wall-to-wall turning radius swept path width rear overhang front overhang turning path width wheelbase acceleration deceleration lean angle vehicle tilt

other dimensions

headlight height elevation angle of headlight beam Corresponding power to weight ratio of design vehicle. As per local requirement off-tracking acceptable walking distance

End of table


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3. ROAD USERS Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Level 3 parameters

driver type

driver type and time of day

norm-day truck-day norm-night truck-night mean-day mean-night skill-day skill-night

cyclist type

primary school children secondary school children recreational cyclists commuter cyclists sports cyclists users of specialist equipment

pedestrian type

commuter shopper /leisure walker disabled person wheelchair users child

dimensions

driver perception time driver reaction time

brake reaction time by use of parameter by typical road condition

driver comfort

sag vertical curve

driver discomfort

centrifugal acceleration

driver deceleration driver's view of the road pedestrian perception time pedestrian reaction time eye height

pedestrian eye height cyclist eye height horse rider eye height driver eye height


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objects

object type object height

general lower object height upper object height object height by type of sight distance

traffic flows

AADT average annual daily traffic 2-way AADT design year flow ADT average daily traffic

general current year ADT design year ADT

design hourly volume DHV DHV design year 30th highest hourly traffic volumes DHV design year 100th highest hourly traffic volumes DRF design reference flow design hour design year K factor traffic composition traffic flow by direction peak hour factor ("peaking factor") design year annual average daily truck traffic (AADTT) traffic index peak hour traffic (PH) protected single equivalent axle loads (ESALs) lane distribution factor bicycle volume (12 hour two-way) pedestrian flow as a percentage of vehicle and pedestrian flow pedestrian flow (pedestrians / hour) other

point rating system for prioritising sidewalks pedestrian environmental factor percent time spent following (PTSF)

End of table


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4. GEOMETRICS 4.1 Speed Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

design speed

general

Level 3 parameters

assumed design speed average design speed average running speed design speed high design speed minimum design speed design speed and road type design speed by terrain type design speed, wet conditions design speed and vehicle type bicycle design speed pedestrian design speed design speed by layout constraint and bendiness design speed and posted speed design speed and 85%ile speed design speed ranges percentile speeds

60%ile speed V50(wet) V85(wet) 85%ile speed 98%ile speed

speed ranges

high speed intermediate speed low speed

other speed parameters

advisory speed anticipated operating speed anticipated speed anticipated speed limit


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Page 4-11


approach speed appropriate speed assumed speed average cruise speed average highway speed average running speed average passing speed average speed average speed of trucks average spot speed average travel speed average vehicle speed balance speed base free flow speed BFFS closing speed constant speed crawl speed crawling speed critical speed cruising speed desirable speed desired speed differential speed differential speed limit effective speed factor entry speed expected speed free-flow speed free speed harmonic mean speed highway speed initial speed legal speed link speed limiting curve speed macroscopic mean speed mainline design speed


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maximum safe speed mean speed mean free operation speed in wet conditions mean free speed microscopic mean speed midblock running speed minimum speed minimum tolerable speed network speed operating speed operating speed of trucks operational speed optimum speed overall speed overall travel speed pace pace speed passing speed posted speed potential speed progression speed ramp design speed recommended speed regulatory speed running speed safe descent speed safe speed satisfactory speed section operating speed space mean speed speed choice speed difference speed differential speed environment speed limit spot speed statutory speed


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statutory speed limit time mean speed target speed travel speed truck speed truck approach speed turning speed undesirable speed differential End of table


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Page 4-14


GEOMETRICS 4.2 Control elements Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Level 3 parameters

factor of safety control lines

grade line superelevation axis of rotation profile grade line vertical alignment control line horizontal control line horizontal alignment control line access control line tangent profile control line point of rotation theoretical grade line baselines True control line Pegged control line pegged base control line axis of rotation

general Rotation about the centerline profile of traveled way Rotation about the inside-edge profile of traveled way Rotation about the outside-edge profile of traveled way Rotation about the outside-edge profile of traveled way when the

horizontal sightline offset control checks

length/sight distance ratio

for horizontal curves

compound curve check

do not use

check sag vertical curves through underpasses


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Page 4-15


design rules other

checklists design briefs


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Page 4-16


4. GEOMETRICS 4.3 Horizontal alignment Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

acceleration

rate of acceleration

Level 3 parameters

acceleration on straights acceleration due to gravity acceleration capabilities of overtaking vehicles acceleration by vehicle type

bicycle acceleration bus acceleration car acceleration truck acceleration

acceleration and weather acceleration and road surface acceleration by road type centrifugal acceleration centripetal acceleration rate of increase of centripetal acceleration radial acceleration lateral acceleration critical lateral acceleration (rollover threshold) rate of change of lateral acceleration rate of increase of lateral acceleration maximum rate of change in lateral acceleration vertical acceleration acceptable vertical acceleration vertical acceleration varies with design speed average acceleration of vehicle in starting gear deceleration


deceleration

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longitudinal deceleration

Page 4-17


deceleration by vehicle type

car deceleration bus deceleration truck deceleration

deceleration by road type deceleration and weather deceleration and road surface coefficient of deceleration

for comfort

deceleration rate rate of deceleration average deceleration comfortable deceleration driver deceleration freewheeling deceleration minimum deceleration desirable minimum deceleration maximum deceleration maximum deceleration rate deceleration distance deceleration on curves by type of vehicle straights

also known as tangents length of tangents

maximum lengths of straights length of straights between circular curves turning in the same direction length of straights between the end and the beginning of reverse circular curves, with no transition curve

circular curves degree of curvature maximum degree of curvature curve radius mimimum curve radius horizontal curve length length of a plain circular curve minimum length of a horizontal curve


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lane widening on curves

by type of vehicle minimum widening extra width for difficulty of driving travelled way widening

maximum tangent deflection angle unit chord plan transition shift distance plan transition length transition curves

transition length

transition length for alignment transition length for crossfall transition length for widening

calculation of....

rate of pavement rotation

reverse transition curves parabolic curve spiral curve clothoid curve several step compound arc spiral curves

minimum length of spiral minimum lateral offset between the tangent and circular curve maximum length of spiral desirable length of spiral length of superelevation runoff maximum radius length of spiral desirable length of spiral deflection angle (angle of deflection) unit chord spiral ray

tangent runout other curves

length of tangent runout

transition curves successive curves compound curve reverse curve bendiness deflection angles


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Page 4-19


overturning criteria vehicle clearance friction longitudinal friction

coefficient of friction for wet pavements and average tires

transverse friction (side friction, lateral friction) high side friction low side friction side friction by vehicle type side friction by road type limiting value of side friction other

skid resistance pavement friction tyre friction methods for distributing side friction and superelevation

sight distance

sight distance and vehicle type

bicycle stopping sight distance pedestrian sight distance

minimum sight distance motor vehicle sight distance sight distance types

anticipatory sight distance (same as decision sight distance) approach sight distance barrier sight distance centreline barrier sight distance decision sight distance emergency stopping sight distance full overtaking sight distance FOSD gap acceptance sight distance for pedestrians horizontal sight distance harmonic mean visibility headlight sight distance horizontal curve perception sight distance horizontal sight distance horizontal curve sight distance Intermediate sight distance intersection sight distance


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"x" value "y" value intersection sight triangle approach sight triangle departure sight triangle meeting sight distance merge sight distance

by speed and vehicle type

manoeuvre sight distance meeting sight distance minimum gap sight distance MGSD overtaking continuation sight distance overtaking establishment sight distance overtaking sight distance passing sight distance perception sight distance

horizontal curve perception sight distance

visibility at roundabouts

forward visibility required at entrance visibility to the left at entry approach visibility visibility of the circulatory carriageway

safe intersection sight distance sight distance to start of auxiliary lane by speed sight distance and overhead obstruction sight distance to the start of an auxiliary lane sight distance and lateral obstruction sight distance with no line of sight sight distance at undercrossings stopping sight distance SSD

SSD and limiting values single lane roads passenger cars, level grade passenger cars, downgrade adjustment SSD for trucks


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Page 4-21


SSD and design speed SSD and deceleration rate SSD and driver eye height SSD and grade SSD and object height SSD and road surface SSD and vertical curvature crossfall (cross slope) adverse crossfall normal crossfall

by road surface

minimum crossfall

by road surface

minimum crossfall

by road element (e.g. bridges)

maximum crossfall

by road surface

roll-over maximum roll-over application of crossfall crossfall transition length carriageway crossfall single crossfall crossfall and road surface crossfall and road element shoulder crossfall auxiliary lane crossfall crossfall and level crossings median crosfall footpath crossfall crossfall in urban areas camber

may be the same as crossfall) negative camber

cross slope

may be the same as crossfall) rate of change of cross slope cross slope and bridges cross slope and road surface differences in cross slope cross slope and cross-secton elements

cross section and medians cross slope and shoulders cross slope and bike paths


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Page 4-22


cross slope and grade unidirectional cross slope superelevation

superelevation - limiting values

minimum superelevation limiting value of superelevation maximum superelevation adverse superelevation

superelevation by type of road

urban road rural road

superelevation and length

superelevation transition length length of superelevation development design superelevation development lengths

superelevation runoff

length of superelevation runoff adjustment factor for supererlevation runoff location of superelevation runoff

superelevation / other

rate of rotation of pavement tangent runout shoulder rollover shoulder slope shoulder direction of slope horizontal clearance

3D design

limit (maximum value) of pseudogeodesic curvature the maximum acceptable value concerning the dynamic superelevation rate

End of table


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Page 4-23


4. GEOMETRICS 4.4

Vertical alignment

Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Level 3 parameters

grade

limiting values

maximum gradient maximum relative gradient max grade by speed, terrain type minimum gradient

variations with road type or section grade at intersections grade by road type length of grade

maximum length of grade critical length of grade

longitudinal slope relative longitudinal slope

between two edges of travelled way between median edge and centreline centreline of each travelled way outside edges of the travelled way

momentum grade relative grade relative gradient grade change

maximum without vertical curve rate of change of grade algebraic difference in grade

vertical tangent length allowable grade breaks vertical curves

types of curve

parabolic curves crest curves sag curves reverse curve compound curve broken back curve

curve shape

Unsymmetrical Vertical Curve parabolic vertical curve


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Page 4-24


curve length

curve length minimum curve length

K values

crest K value sag K value K value by road type and design speed

other

VPC (Vertical Point of Curvature) PRC point of reverse curvature VPI (Vertical Point of Intersection) VPT (Vertical Point of Tangency) distance between vertical curves

vertical clearance

limiting values

minimum vertical clearance preferred vertical clearance

static clearance effective clearance clearance by road type clearance by type of utilities clearance by type of vehicle clearance by type of structure

vehicle bridges pedestrian bridges

clearance below vehicle vertical clearance and weather vertical clearance and road maintenance

End of table


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Page 4-25


4. GEOMETRICS 4.5

Cross-section


Level 2 parameters

traffic lanes

standard traffic lane

Level 3 parameters

managed lanes

HOV lane

ramps

emergency escape ramp

vehicle specific lane

bus lane truck only lane bicycle lane bicycle path pedestrian ways sidewalks

parking lanes

parallel parking angled parking centre of road parking truck parking motorcycle parking disabled parking

auxiliary lanes

speed change lanes merge lane diverge lane overtaking lane climbing lane partial climbing lane slow vehicle turnout storage lane passing lane passing section descending lane weaving lane continuous auxiliary lane two-way, left-turn lanes (TWLTL) (flush-type median); Tram/Light Rail Vehicle (LRV) Lanes


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Page 4-26


left turn lane at junction right turn lane at junction dedicated right turning lane median

median type

concrete barrier depressed median flush median curbed median median barrier raised curb median traversable median painted flush median median width median slope

median edge strip median island median crossovers central reserve shoulders

hard shoulder inside shoulder inner shoulder outer shoulder shoulder width by function shoulder width by speed and traffic flow shoulder break point

separators

outer separator (for service lane) outer separations

verges

general verge width

verge width by function

verge slope verge rounding edges, strips

edge clearance side strip edge strip median edge strip rumble strip landscaping strip

curbs


curbed roadways

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Page 4-27


uncurbed roadways curb and channel type of curb special use elements

rest area scenic overlook brake check area brake rest area slow vehicle turnout turnout passing bay vehicle specific elements

bus stop tram stop

horizontal clearance

clear width for structures speed reduction clear width sight distance clear width

(line of sight)

clear zone lateral offset for vertical structures shy distance buiilding offset right of way (ROW) widths

right of way lines right of way width intersection sight distance ROW property lines

overall widths

travelled way width roadway road reserve road prism road bed travelled way carriageway clear zone clear roadway width side clearance

other

shy line grade break for shoulders berm batter


March 2017

batter slope

Page 4-28


batter rounding benches side slopes clear zone buffer area nature strip urban border general

width of elements

desired width minimum width maxmum width acceptable width sufficient width effective width appropriate width standard width

widths and road type widths and road elements

tunnels

widths and design speed

lane widths

number of elements

End of table


March 2017

Page 4-29


4. GEOMETRICS 4.6

Junctions


Level 2 parameters

interchanges

over

Level 3 parameters

under free-flow interchange standard grade-separated interchange diverging diamond interchange compact grade-separated junction full diamond half cloverleaf full cloverleaf two-level dumbell roundabout five-bridge three-level roundabout two-bridge two-level roundabout access interchange cloverleaf interchange partial cloverleaf quarter link systems interchange trumpet interchange 3-level roundabout trumpet junction grade-separated roundabout single-point junction mode specific interchanges

pedestrian overbridge pedestrian underpass Grade-Separated Pedestrian Crossings

intersections

3-leg intersection 4-leg intersection T-intersection Y-type Scissor type


March 2017

Page 4-30


Cross-type staggered (left/right) staggered and skewed (right/left) multiway simple T junction staggered T junction crossroads junction roundabout intersections - types

normal roundabout mini roundabout double roundabout ring intersection signalised roundabout grade-separated roundabout dumbell roundabout two-bridge roundabout

signalised intersections - types

signal-controlled intersections signalised intersections signalised junctions

other intersections - types

Restricted Crossing U-Turn Intersection Median U-Turn Intersection Displaced Left Turn Intersection Diverging Diamond Interchange accesses

mode-specific intersections

pedestrian crossings

priority junction

major/minor priority junction single lane dualling urban simple junction rural simple junction

junction details ghost island junction turning length deceleration length taper length single lane dualling roundabout details


March 2017

inscribed circle diameter

Page 4-31


entry angle entry width approach half width average effective flare length entry radius entry path radius flare sharpness average flare length merging tapers interchange details

interchange ramps exit ramp ramp terminal single lane exit two-lane exit lane split length acceleration distance

other

visibility splays access control junction spacing access ramps

on ramps off ramps

junction frequency

number of access points / km

ramp junction left-right staggered junction right-left staggered intersection right-left staggered junction left-right staggered intersection T intersection T junction trumpet interchange trumpet junction Y intersection Y junction terminal junction junctions and road types

rural motorway junction urban grade-separated interchange


March 2017

Page 4-32


rural grade-separated interchange weaving length and road type End of table


March 2017

Page 4-33


4. GEOMETRICS 4.7

Parking


Level 2 parameters

Level 3 parameters

parking types

parking and vehicle type

car parking cycle parking disabled parking parent and child parking parking for caravans and trailers truck parking parking and pedestrians

parking and purpose

airport parking supermarket parking commuter parking residential parking

parking and location

on-street

surface parking multi-storey parking other

parking and comfort parking and user class

parking elements

stalls

stall length stall width stall angle

aiisles

one-way aisles two-way aisles parking aisles circulation aisles

ramps

gradient superelevation width ramp types ramp visibility turning circles

clearances


March 2017

side clearance

Page 4-34


column location headroom ramp clearances ramp transitions other

wheel stops

End of table


March 2017

Page 4-35


5. GEOGRAPHY Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

terrain types

topography

Level 3 parameters

difficult terrain escarpment flat terrain flat rolling hilliness intermittent level mountainous terrain rolling terrain rugged terrrain steep terrain undulating terrain Number of 5 metre contours crossed per km terrain and other parameters

terrain and maximum superelevation terrain and maximum grade terrain and cost terrain and design speed terrain and capacity terrain and vehicle types terrain and superelevation

development

urban Central Business Districts (CBD) Fringe Area/Outlying Business District (FRNG/OBD) suburban open-suburban closed suburban rural unpopulated rural area semi-rural area


March 2017

Page 4-36


natural corridors developing corridors city / town centres (rural main streets) rural area

natural village developed

suburban area

high density town centre low density

urban area

urban park urban residential central business district

peri-urban areas climate types

snow and ice conditions

hill roads in snow-clad areas

icy conditions desert regions monsoon

hill roads in monsoon

rainfall total annual rainfall

rainfall class

pavement climate regions severe winter conditions semi-arid climate temperatures climate with other parameters

weather

affect on friction affect on visibility climate and superelevation climate and cross-section

environment

flora fauna noise air quality impact on water resources water quality ground water quality soils


March 2017

soil erosion

Page 4-37


soil contamination cultural heritage tourism and agriculture End of table


March 2017

Page 4-38


6. ECONOMICS Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Economics

maintenance cost

Level 3 parameters

capital cost user cost vehicle operating cost Economics and other parameters

cost and width of shoulders cost and median width cost and object height cost and overtaking zones cost and grade cost and right of way cost and superelevation cost and widening cost and crest vertical curves cost and lane width cost and shoulders in tunnels cost by type of terrain cost and length of passing sections

End of table


March 2017

Page 4-39


7. ENGINEERING Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Level 3 parameters

drainage

minimum cover over cross-drainage structure

Engineering

drainage control table drains catch drains median drains earthworks

height of embankment

utilities

type and location of utilities

road pavement

road surface rolling resistance of surfacing materials

Engineering and other parameters

engineering and minimum grade independent design of carriageways surface material

surface material and crossfall surface material and rolling resistance shoulder mateirial and crossfall surface material and crossfall

cross-section

material and side slopes

right of way

material and side slopes

End of table


March 2017

Page 4-40


8. AESTHETICS Note that this table only shows the first three levels of paramaters. Level 1 parameters

Level 2 parameters

Aesthetics

Coincident Horizontal and Vertical Curves

Level 3 parameters

rural visual impact earthworks

Reducing Earthwork Modification

erosion control urban visual impact curvilinear alignment general appearance cultural heritage factors Aesthetics and other parameters

aesthetics and design speed aesthetics and axis of rotation aesthetics and roadway drainage aesthetics and minimum horizontal curve length aesthetics and minimum length of vertical curvature on ramps aesthetics and minimum rate of vertical curvature

End of table


March 2017

Page 4-41


9. CONCEPTS Note that this table only shows the first three levels of paramaters. concepts

bicycle network concepts complete streets concept of design speed context sensitive design CSD context sensitive solutions CSS criteria-based design design domain concept desired operating speed extended design domain extended design domain concept factor of safety concept flexibility in design forgiving highway green streets level of service concept main street managed lanes multifunctional road new urbanism nice road normal design domain pedestrian network concepts performance based practical design practical design practical solutions Road Diets (Roadway Reconfiguration) self-explaining road smart growth smart transportation speed environment concept The concept of desired speed walkable communities

End of table


March 2017

Page 4-42

Listing Highway Parameters - Part 5 Definitions

PART 5 - DEFINITIONS


6.1

Overview

6.2

List of definitions


March 2017

Page 5-1

Listing Highway Parameters - Part 5 Definitions

5.1

Overview

Temporary list of definitions for this document.

5.2 List of definitions Term

Definition

Source

Parameter

In the context of the geometric design of roads, a parameter is a definable, quantifiable feature or variable which influences or sets the conditions of the design

Author

Standard

A collection of documents, including all the national and local standards identified in the publication "global standards", and also a large number of technical papers and reports which cover topics in the road design area.

Author

Definition

Either an explanation of the meaning of a parameter, found in a standard or, where an explanation cannot be found, one or more examples of the use of the term.

Author

Junction

A junction is any node in the road network

Author

Interchange

An interchange is a grade-separated junction

Author

Intersection

An intersection is an at-grade junction

Author


March 2017

Page 5-2

Listing Highway Parameters - Part 6 Annexes

PART 6 - ANNEXES


6.1

Glossary (excerpt)

6.2

List of references (excerpt)


March 2017


6.2 List of references (excerpt) Details of references which are referred to in the text..

This is a working list which is presently being updated and reformatted.


March 2017

Listing Highway Parameters / Annex 1 Parameter Group

NMT vehicle type

Reference details Number.

2335

Year

2009

Country

South Africa

Name

Non-motorised transport in the Western Cape

Parameter Group

Urban expressway road type


Year

861

Country Name

Parameter Group

DRAFT

Non-motorised transport (NMT) includes all forms of transport that are human- or animal powered. Examples of NMT for personal mobility include walking, cycling, perambulating, rollerblading, skateboarding, bicycle taxiing rickshaw riding and horse riding. There are also NMT modes for transport of goods, including wheel barrows and carts drawn by donkeys, horses or humans. Importantly, NMT modes include wheelchairs, and hence must be a consideration when planning and designing transport related facilities for special needs persons

Urban expressways are generally high-speed, limited access facilities whose function is to move both inter-urban and intra-urban traffic. Mobility is a high priority. Expressways may often serve as major freight corridors as well as being designated as an OHP Freight Route. They are often part of the National Highway System (NHS). Private property access is discouraged in favor of through mobility importance. Access is normally restricted to atgrade signalized and unsignalized public road intersections or interchanges. At-grade signalized intersections may provide full access. However, at-grade, unsignalized intersections should be considered carefully and for safety

Design speed is a selected speed used to determine the various geometric design features of the roadway.

Design speed speed

Reference details Year

2016

Country

USA

Name

Illinois BDE Manual

Parameter Group

Number.

2327

Rural area geography


2016

Country

USA

Name

Illinois BDE Manual

Number.

2327

Urban areas. Those places identified by the US Bureau of Census as having a population of 50,000 or more (urbanized areas) or 5,000 or more but less than 50,000 (small urban areas); all places outside of urbanized and small urban areas are rural areas.


Urban areas. Those places identified by the US Bureau of Census as having a population of 50,000 or more (urbanized areas) or 5,000 or more but less than 50,000 (small urban areas); all places outside of urbanized and small urban areas are rural areas.

Urban area geography


2016

Country

USA

Name

Illinois BDE Manual

Parameter Group

Number.

2327

Design speed speed


Year

2010

Country

multi-c / Austroads

Name

AGRD part 3: Geometric design

Parameter Group

1887

A speed fixed for the design and correlation of those geometric features of a carriageway that influence vehicle operation. Design speed should not be less than the intended operating (85th percentile) speed. If the operating speed varies along the road, the design speed must vary accordingly.

A compilation of the 85th percentile values of the various parameters of the vehicle type being designed for, e.g. length, width, wheelbase, overhang, height, ground clearance, etc

Design vehicle vehicle


148

Year

2002

Country

South Africa

Name

GDG - Geometric design guidelines, published by CSIR

Parameter

DRAFT

A compilation of the 85th percentile values of the various parameters of the vehicle type being designed for, e.g. length, width, wheelbase, overhang, height, ground clearance, etc., and not a commercially available vehicle.

Design vehicle

Group


2247

Year

2015

Country

South Africa

Name

Geometric design of roads handbook


Rainfall assessment geography


728

Year

2009

Country

Lao

Name

Laos, low volume rural road environmentally optimised design manual

Parameter Group

geography

Number.

728

Year

2009

Country

Lao

Name


Group

The climate of a region affects the design of a road, from the materials that can be used to the need to seal a gravel surface on a hill. Although there are many aspects of climate – total rainfall, duration of wet season, rainfall intensity, etc – in this manual climate is represented by the total annual rainfall.

Terrain with minimal gradient and minimal restriction on horizontal and vertical alignment. Number of 5 metre contours crossed per km = 0 to 10

Flat terrain

Reference details

Parameter

DRAFT

Terrain with low hills and some restrictions on horizontal and vertical alignment. Number of 5 metre contours crossed per km = 11 to 25

Rolling terrain geography


728

Year

2009

Country

Lao

Name


Parameter Group

Terrain with steep hills and substantial restrictions on horizontal and vertical alignment. Number of 5 metre contours crossed per km > 25

Mountainous terrain geography


728

Year

2009

Country

Lao

Name


Listing Highway Parameters / Annex 1 Parameter

Environmentally Optimised Design

Group


2009

Country

Lao

Name


This appears to be (a) where the sum of the final year AADTs of traffic categories 3 and 4 is < 150 and there are no vehicles in category 5. Category 3 is light 4-wheeled motor vehicles, category 4 is medium 4-wheeled motor vehicles and category 5 is heavy 4-wheeled motor vehicles

Low volume rural road

Group


728

Year

2009

Country

Lao

Name


Parameter

Low volume roads

Group


Year

The Environmentally Optimised Design (EOD) approach. With this approach, the road is designed to suit a variety of task and environmental factors such as rainfall, available materials, construction capacity, gradient, flood risk and so on.

728

Year

Parameter

DRAFT

1100

Country

The criteria for defining a “Low-volume road” varies significantly in various parts of the world. In the SADC region, such roads may be primary, secondary or tertiary/access roads. They typically carry less than 200 vehicles per day, including up to 20% commercial vehicles, and often include non-motorised traffi c, particularly near populated areas.

Name

Parameter Group

A Wide Single 2+1 (WS2+1) road consists of two lanes of travel in one direction and a single lane in the opposite direction. This provides overtaking opportunities in the two lane direction, while overtaking in the single lane direction is prohibited.

Wide Single 2+1 (WS2+1) road road type


1409

Year

2008

Country

UK

Name

DMRB 6 section 1 part 4 (TD 70/08 Design of Wide Single 2+1 Road)


A portion of the roadway which has been designated by road markings, striping and signing as being exclusively for the use of cyclists

Cycle lane geometrics - cross-section

Reference details

see also bicycle lane, bike lane Number.

148

Year

2002

Country

South Africa

Name


Parameter Group

Design speed speed


Year

2010

Country

multi-c / Austroads

Name


Parameter Group

1887

Operating speed (85th percentile speed) speed


Year

2010

Country

multi-c / Austroads

Name


Parameter Group

DRAFT

A speed fixed for the design and correlation of those geometric features of a carriageway that influence vehicle operation. Design speed should not be less than the intended operating (85th percentile) speed. If the operating speed varies along the road, the design speed must vary accordingly.

The term Operating Speed in this guide refers to the 85th percentile speed of cars at a time when traffic volumes are low, and drivers are free to choose the speed at which they travel. In effect, this means that designs based on the 85th percentile speed will cater for the majority of drivers.

1887

For design purposes, the following definitions of high, intermediate and low vehicle speeds will apply for both urban and rural areas:

High vehicle speed speed

Reference details

High speed: 90 km/h or greater Number.

Year

2010

Country

multi-c / Austroads

Name


1887

- Intermediate: 70 km/h to 89 km/h - Low speed: 69 km/h or less



Intermediate vehicle speed speed

Reference details

- High speed: 90 km/h or greater Number.

Year

2010

Country

multi-c / Austroads

Name


Parameter Group

1887

speed

- High speed: 90 km/h or greater Number.

Year

2010

Country

multi-c / Austroads

Name


1887

Freeways

Group


Year

2010

Country

multi-c / Austroads

Name


Parameter



Low vehicle speed

Reference details

Parameter

DRAFT

1887

Group


2010

Country

multi-c / Austroads

Name


These are roads that are intended to provide a high quality of service for high traffic volumes, and need not be designated as freeways (some road authorities refer to these roads as motorways).They are characterised by having full control of access, median divided multi-lane carriageways, grade separations and interchanges. Vertical alignments tend to have flatter grades in order to minimise the difference in speed between cars and trucks.

Stopping Sight Distance (SSD) is the distance to enable a normally alert driver, travelling at the design speed on wet pavement, to perceive, react and brake to a stop before reaching a hazard on the road ahead.

Stopping sight distance SSD

Year


1887


DRAFT

A speed selected to establish specific minimum geometric design elements for a particular section of highway or bike path.

Design speed speed


2360

Year

2016

Country

USA

Name

California highway design manual 2016

Parameter Group

Limiting curve speed speed


2362

Year

2007

Country

Australia

Name

Queensland RPDM 1st edition / chapter 6 speed parameters

Parameter Group

Design speed speed


2006

Country

UK

Name

textbook

Number.

1038

The limiting curve speed is the speed at which a vehicle travelling on a curve of given radius and superelevation, will have a side friction demand equal to the absolute maximum recommended value given in Chapter 11 (Horizontal Alignment), for that speed.

A fundamental consideration in the design of a road section is the design speed to be used. Notwithstanding the apparent simplicity of the term 'design speed' there is still argument over its exact definition. In practice, however, it simply means the speed value used as a guide by road designers when determining radii, sight distances, superelevations, and transition lengths. n most design guides, the selection of design speeds for road sections of a particular classification is primarily influenced by the nature of the terrain (e.g. whether level,

Parameter

Traffic flow

Group


148

Year

2002

Country

South Africa

Name


Traffic flows vary both seasonally and during the day. The designer should be familiar with the extent of these fluctuations to enable him or her to assess the flow patterns. The directional distribution of the traffic and the manner in which its composition varies are also important parameters. A thorough understanding of the manner in which all of these behave is a basic requirement of any realistic design.


Thirtieth highest hourly flow

Group


148

Year

2002

Country

South Africa

Name


Parameter

peak hour factor ("peaking factor")

Group


148

Year

2002

Country

South Africa

Name


Parameter Group

Reference details 2011

Country

USA

Name

AASHTO, A policy on the geometric design of highways and streets 2011

Lane distribution factor

Group


To predict hourly flows, it is necessary to know the ADT and the peaking factor, ß. The parameter, ß, is a descriptor of the traffic flow on a given road and depends on factors such as the percentage and incidence of holiday traffic, the relative sizes of the daily peaks, etc. The peaking factor can fluctuate between -0,1 and -0,4.

831

Year

Parameter

If hourly flows are ordered from highest to lowest, it is customary, in rural areas, to design for the thirtieth highest hourly flow, i.e that flow which is exceeded in only 29 hours of the year.This is because rural roads have very high seasonal peaks and it is not economical to have a road congestion-free every hour throughout the year. In urban areas, seasonal peaks are less pronounced and the 100th highest hourly flow is considered a realistic flow level for design purposes.

The ADT is defined as the total volume during a given time period (in whole days), greater than one day and less than one year, divided by the number of days in that time period..

ADT average daily traffic

Number.

DRAFT

2360

Year

2016

Country

USA

Name


Truck/bus traffic on multilane highways normally varies by lane with the lightest volumes generally in the median lanes and heaviest volumes in the outside lanes. Buses are also typically found in HOV lanes. For this reason, the distribution of truck/bus traffic by lanes must be considered in the engineering for all multilane facilities to ensure that traffic loads are appropriately distributed.


DRAFT

The Traffic Index (TI) is a measure of the number of ESALs expected in the traffic lane over the pavement design life of the facility.

Traffic index (TI)

Group


2360

Year

2016

Country

USA

Name


Parameter

The annual average daily traffic (AADT) is the total volume of traffic for the whole year divided by the number of days in the year.

AADT

Group


57

Year

2002

Country

Australia

Name

Queensland RPDM 1st edition / chapter 5 (superceded)

Parameter

The "Australian Model Code for Residential Development (AMCORD), November 1990 .... defines local streets as having traffic volumes up to 2,000 vpd.

Local streets

Group


57

Year

2002

Country

Australia

Name


Parameter Group

These are roads that are designed for operating speeds in excess of 90 km/h. This may include freeways, which are intended to provide a high quality of service for large traffic volumes.

High speed rural roads speed


Year

2010

Country

multi-c / Austroads

Name


1887


Intermediate speed rural roads

Group


Year

2010

Country

multi-c / Austroads

Name


Parameter Group

1887

Low speed rural roads speed


Year

2010

Country

multi-c / Austroads

Name


Parameter

Operating speed of trucks

Group

1887


2010

Country

multi-c / Austroads

Name


Parameter Group

Vehicle speeds on a series of curves and short straights tend to stabilise at a value related to the range of curve radii. This speed is called the ‘Section operating speed’.

speed


2010

Country

multi-c / Austroads

Name


These are roads having many curves with radii less than 150 m. Operating speeds on the curves generally vary from 50 – 70 km/h. Rural roads usually only have these characteristics when difficult terrain and costs preclude the adoption of higher standard geometry. The alignments provided in these circumstances could be expected to produce a high degree of driver alertness, so those lower standards are both expected and acceptable. These roads often have a reduced speed limit (typically 60 to 80 km/h), which helps to lower the desired speed (Table 3.2). As with intermediate speed rural roads, drivers will slow down for horizontal curves

1887

Section operating speed

Year

Minimum operating speeds on these roads are generally constrained by the geometry to about 70 – 90 km/h. Drivers will however, accelerate whenever the opportunity arises, such as on any straight or large radius curve. Speeds will increase up to the desired speed where possible, which may be up to 110 km/h (Table 3.2). Horizontal curve radii on these roads are generally in excess of 160 m, and the vertical alignment usually has little effect on operating speeds.

The term ‘Operating Speed of Trucks’ is the 85th percentile speed of trucks at a time when traffic volumes are low. In many places, the operating speeds of cars and trucks will be different due to their performance characteristics, especially on grades.

speed

Year

DRAFT

1887


6.1 Glossary (excerpt) Collection of definitions of terms / parameters related to the geometric design of roads.

Definitions may or may not be accepted, up-to-date, or correct. The glossary in the following pages is an excerpt from a more extensive document, and refer to the “Speed” sub-group of parameters. They are taken from English-language standards only at this stage.


March 2017

Listing Highway Parameters / Annex 2

DRAFT

Ref.

Country

Year

Title

Publisher

57

Australia

2002


59

UK

2002

Design recommendations for multi-storey and underground car parks (3rd ed)

61

UK

1973

"Roads in urban areas (3rd edition)", London, HMSO 1973

74

New Zealand

2005

Transit, State highway geometric design manual part 4 - horizontal alignment

Transit New Zealand

80

New Zealand

2003

Transit, State highway geometric design manual part 2 - basic design criteria

Transit New Zealand

93

India

1991

IRC: 86 (1983 / 1991) - geometric design standards for urban roads in plains

112

Bangladesh

2000

Geometric design standards for RHD

112

Bangladesh

2000

Bangladesh:Geometric design standards for RHD; draft version 4, October 2000

138

New Zealand

2005

State highway geometric design manual - glossary of terms

Transit New Zealand

148

South Africa

2002


CSIR

157

USA

2010

Texas roadway design manual

167

UK

1974

Hobbs- Traffic planning and engineering (1974)

Institute of Structural Engineers

Listing Highway Parameters / Annex 2 Ref.

Country

Year

DRAFT

Title

Publisher

255

UK

2002

DMRB 6 section 1 part 1/ TD 9/93 highway link design

293

India

2000

IRC: 73 (1980 / 1990) - geometric design standards for rural (non-urban) highways.

294

Tanzania

2001

Tanzania, "Road geometric design manual, 2011 edition", Ministry of Works, Dar es Salaam; 2012

408

Iraq

1982

Iraq, Highway design manual, published by the road and traffic division of the Ministry of Housing and Construction.

508

Nepal

2012

Nepal, DoLIDAR, "Nepal Rural Roads Standards 2012-1st revision"; Nepal 2012

584

USA

2012

Roadway design guidelines, Arizona DoT

585

Australia

2011

VicRoads supplement part 3 - geometric design

VicRoads

587

Ireland

2003

Highway engineering

Blackwell Science

635

UK

1998

"Overseas road note 6, A guide to geometric design” England, TRL 1988

TRL

636

Laos

2008

Seacap 3: Laos, low-volume rural road standards....

713

USA

1994

AASHTO - A policy on geometric design of highways and streets 1994

714

Italy

2001

Ministro delle Infrastruture e dei Trasporti, "Norme funzionali e geometriche per la costruzione delle strade", Decreto Ministeriale 5, November 2001

Ministry of Works


Country

Year

DRAFT

Title

726

multi-c UNECE

2002

UNECE "Trans European Motorway standards and recommended practice third edition", Poland 2002

727

Romania

2005

"Design manual for low cost rural roads in Romania" IBRD February 2005

728

Lao

2009


732

Switzerland

1991

VSS 640-080 Projektierung, Grundlagen (basics of road design

734

Italy

1980

CNR - Bolletino Ufficiale (Norme tecniche) A XIV - N 78

744

UK

2005

DMRB UK TA 90-05 geometric design of pedestrian, cycle and equestrian routes

756

Asia

2003

Asian highway handbook, full version 2003

762

Canada

2011

Canada, " December 2011 Updates to the Geometric Design Guide for Canadian Roads", TAC 2011

763

Malaysia

1986

Malaysia, "A guide on geometric design of roads", 1986

769

Nepal

771

multi-country

2001

SATCC "Draft code of practice for the geometric design of trunk roads", CSIR, South Africa 2001 (SATCC = Southern African Transport and Communications Commission)

777

USA

2013

University of Idaho, webpage with notes on "superelevation and side friction", downloaded July 2013

Publisher

Roads Branch, Public Works Department

RAIDP technical manual vol.1, downloaded July 2013

CSIR


Country

778

Year

DRAFT

Title

Publisher

2011

779

Malaysia

2002

Malaysia, REAM "A guide on geometric design of roads" (2002 update); 2002

781

USA

2003

The Civil Engineering Handbook, Second Edition; edited by W . F . Chen and J . Y . Richard Liew, CRC Press 2002

782

USA

2002

Banks, "Introduction to Transportation Engineering, chapter 4 - geometric design", McGraw Hill Education, 2002

783

Colombia

2010

Henao, John Jairo and others, "The policy on highway geometric design in Colombia", 4th ISHGD, 2010

802

USA

2012

CHRP Synthesis 432 - recent roadway geometric design research

827

USA

2001

A policy on the geometric design of highways and streets 2001

829

USA

2004

Highway engineering handbook

McGraw Hill

831

USA

2011

AASHTO, A policy on the geometric design of highways and streets 2011

AASHTO

833

USA

1996

Highway design manual

834

UK

2007

'Flaherty, Highways (4th edition)

837

Yemen

1986

Yemen Highway Authority, Development of National Highway Master Plan, "Design Standards", prepared by Dar al Handasah, 1986

McGraw Hill Education

Butterworth-Heinemann


DRAFT

Ref.

Country

Year

Title

Publisher

843

Singapore

2010

Civil design criteria for road and rail transit systems

850

Philippines

2011

Road Safety Design Manual

854

Yemen

2004

Yemen, Ministry of public works and highways, rural roads design manual, section 3: geometric standards

856

textbook

2004

Road engineering for development, 2nd ed.

Spon Press

857

Australia

2003

Austroads, "A guide to the geometric design of rural roads (8th ed.)"

Austroads

859

Ireland

2013

Design manual for urban roads and streets (published by the Department of transport, tourism and sport).

891

USA

2012

Highway design manual chapter 2 - design criteria, NYSDOT

892

multi-c SICA

2011

Manual Centroamericano de Normas para el Diseño Geométrico de Carreteras, 3ª. Edición, 2011

894

Bolivia

2007

Manual de carreteras, vol. 1 / Manual de diseno geometrico

899

Peru

2001

DG-2001: Manual de Diseño Geométrico de Carreteras (DG-2001) Published by the MTC.

900

Colombia

2008

Manual de Diseno Geometrico de Carreteras from the Ministerio de Transporte

903

Peru

2008

Manual de diseno de carreteras no pavimentadas de bajo volumen de transito


Country

Year

DRAFT

Title

Publisher

917

USA

2011

Los Angeles 2010 bicycle plan, technical design handbook

922

Norway

2008

Hb265: Linjeføringsteori, from the Statens vegvesen NPRA Norwegian Public Roads Administration;

929

Germany

2001

Introduction of a new approach to geometric design and road safety

943

USA

1995

Changes in horizontal alignment standards in Australia and Canada, presented at the International Symposium on Highway Geometric Design Practices, TRB 1995

962

USA

1998

Highway capacity manual, 3rd edition

985

USA

1999

AASHTO Guide for the development of bicycle facilities

1005

Ethiopia

2011

Design manual for low volume roads, part-A

Ethiopian Roads Authority

1010

USA

2004

DelDOT Road design manual 2 - design controls

Delaware DOT

1024

Austria

2010

Anlagen für den nichtmotorisierten Verkehr

1035

Bosnia & HG

2005

Guidelines for road design, construction, maintenance and supervision volume 1.1.3 (volume 1: designing section 1: road designing part 3: geometrical road elements)

1036

USA

2004

Traffic engineering, 3rd edition

Pearson Education International

1038

UK

2006

textbook

Elsevier

20 th South African Transport Conference


Country

Year

DRAFT

Title

1042

Multi-country

2003

SADC / SATCC Guideline on low volume sealed roads

1062

Netherlands

2007

Nieuwe Ontwerprichtlijn Autosnelwegen (NOA)

1063

Ethiopia

2002

Ethiopia, geometric design manual 2002 (version 2); Ethiopian Roads Authority (ERA). component parts downloaded from ERA website and combined on 21.10.2013.

1076

South Africa

2003

Pedestrian and bicycle facility guidelines

1083

Peru

2008

"Manual para el diseño de carreteras pavimentadas de bajo volumen de tránsito", published by the MTC.

1088

SIECA

2004

Manual Centroamericano De Normas Para El Diseño Geométrico De Las Carreteras Regionales

1103

Chile

2009

Manuale de vialidad urbana

1115

Estonia

2000

Estonia Norms and Requirements of Road Design

1155

Albania

2007

ARDM 2 Road design manual vol. 2 / geometric design

1159

Finland

2013

Finland standard 30/2013: Road alignment design (Tien suuntauksen suunnittelu)

1196

Ireland

2011

1252

USA

2002

Publisher SADC / SATCC

NRA

Flexible design of New Jersey's main streets


DRAFT

Ref.

Country

Year

Title

1370

Abu Dhabi

2013

Abu Dhabi, road geometric design manual (manual A9) (3rd ed)

1388

Dubai

2001

Geometric design manual for Dubai roads

1389

Georgia

2009

SST Gzebi:2009 / Georgia road design standards

1396

multi-country

2008

ECE European agreement on main international traffic arteries

1409

UK

2008

DMRB 6 section 1 part 4 (TD 70/08 Design of Wide Single 2+1 Road)

1505

Nigeria

2013

Highway manual part 1 Design / vol. I: geometric design (Federal Ministry of Works)

1555

India

2012

RC / SP: 84 - Manual for standards and specification for four laning laning of state highways on PPP Basis.

1573

USA

2002

Design Speed, Operating Speed, and Posted Speed Limit Practices

1597

Afghanistan

2013

Afghanistan Rural Roads Manual

1615

Germany

2008

FGSV, "RAA Richtlinien für die Anlage von Autobahnen"; hardcopy, purchased 2014.

1617

Germany

2013

Wolf et al, Strassenplanung, Werner Verlag 2013

1623

USA

2014

Caltrans highway design manual

Publisher

TRB 2003 Annual Meeting

California department of transportation


DRAFT

Country

Year

Title

1627

Sweden

2004

Sweden 2004-80 alignment (Vägar och gators utformning Linjeföring)

1635

Australia

1990

Handbook of road technology (2nd edition) vol. 2 "traffic and transport"

1654

Peru

2005

P

1656

India

1976

IRC-66-1976 - recommended practice for sight distance on rural highways

1670

Ecuador

2003

Normas de Diseño Geométrico-2003 MOP

1689

Kenya

1979

Road design manual part 1: geometric design of rural roads

1711

Saudi Arabia

?

Saudi Arabia : HDM 1.2 design of roadways

1738

UK

1990

New metric handbook - planning and design data

1783

USA

1997

"Stopping sight distance and decision sight distance"; Oregon State Uni, TRI

1822

Sri Lanka

1998

Geometric Design Standards of Roads -RDA-1998

1830

France

2000

ICTAAL - Autoroutes (motorways)

1840

multi-c TAH

2013

TAH Annex II Basic Guidelines for Road classification standards (TAH = Trans-African Highways)

Publisher


DRAFT

Country

Year

1860

Argentina

2010

Normas y Recomendaciones de Diseño Geométrico y Seguridad Vial

1884

multi-country

2003

ASEAN highway standards

1885

Multi-country

2010

AGRD part 1: Introduction to road design

Austroads

1887

multi-c / Austroads

2010


Austroads

1888

Multi-country

2006

AGRD part 2: Design considerations

Austroads

1919

USA

2012

California Highway Design Manual 2012

California DOT

1956

Qatar

2013

QHDM Intersections and Interchanges

Qatar

1978

Ethiopia

2013

Geometric Design Manual with appendices Final - Appendix

ERA

2133

Canada

Geometric Design Manual Part 2

Middlesex County, Ontario, Canada

2144

Finland

Helsinki, street cross-sections

Helsinki transport planning department

Geometric design and safety for LVRR

AFCAP /UKAID

Geometric design of roads handbook

CRC Press

2001

2211

2247

South Africa

2015

Title

Publisher


Country

Year

DRAFT

Title

Publisher

2326

Netherlands

2015

Insight in horizontal curves

2327

USA

2016

Illinois BDE Manual

2335

South Africa

2009

Non-motorised transport in the Western Cape

2351

Philippines

2000

Design standards for tourism and farm to market roads

2352

UK

2000

Industrial & commercial estate roads

2353

UK

2001

Industrial roads design guide

2357

Canada

2004

Waterloo region, active transportation master plan

2360

USA

2016


2362

Australia

2007

Queensland RPDM 1st edition / chapter 6 - speed parameters

2371

USA

2006

Massachusetts Project development and design guide

2380

Australia

2016

MRWA supplement to Austroads guide to road design - part 3

MRWA

2381

UK

2008

Kent design guide - supplementary-guidance-visibility

Kent CC

Illinois DOT

TAP Transport Advice Portal


Country

Year

DRAFT

Title

2382

USA

2013

A Sample of Green Streets Definitions

2383

South Africa

2010?

Complete Streets Design Guideline Manual

2385

USA

2010

Designing Walkable Urban Thoroughfares: A Context Sensitive Approach

2386

USA

2015

Evolving Geometric Design Decision-Making in the United States

2387

USA

2009

Rule-Based Road Design using AutoCAD Civil and AutoCAD Civil 3D

2395

USA

2013

Florida green book, FDOT

2396

USA

2415

USA

2008

Smart transportation guidebook 2008

9001

Canada

2016

TDM Encyclopedia (online document)

Publisher

Glossary of road design and construction terms, Nebraska DOT

New Jersey DOT