Unification of highway design standards

Unification of highway design standards (UHDS) is an idea which would seem both sensible – and also ridiculous. Sensible, because the same basic road vehicles and the same road materials can be found all around the world; but ridiculous, because perhaps driving conditions are different on the sand-strewn roads of Saudi Arabia, the low temperatures of winter roads in Iceland, and the very busy roads of central London.

The answer to the objection that conditions are different  in different countries is that a wide range of driving conditions can be found within one country. Sandy roads, low temperature roads and busy roads can all be found in (for example) the USA and Peru.

There might be two advantages of trying to create documentation on UHDS:

  • Simplifying the search for  design parameters such as side friction when designing horizontal road curves
  • Bringing out examples of innovative and best practice

Number of existing standards

In theory there is a limited number of standards in the world  – one for each country. If there are 180 countries in the world, there will therefore be only 180 highway design standards. Here, the first problem is that there seems to be uncertainty about how many countries there are. One Wikipedia page lists countries by GDP (link) – but it has four lists, with the total number of countries shown variously as  184, 192 and 194.

Perhaps the World Atlas list, with 192 countries (see here) would be as good a place as any to start.

Fewer standards

In fact, there might be fewer than 192 standards (the figure assumes one per country). Some of the smaller countries may base their road standards entirely on those from a large country such as the USA. There are also groups of countries which are working on regional standards such as the East African Community and the UNECE (United Nations Economic Commission for Europe). For example the UNECE has published common geometric standards for trans-European motorways; and a World Bank document on the “Southern Africa Development Community Protocol on Transport, Communications and Meteorology” (link) says that: Member States agree to develop appropriate harmonised technical standards in respect of amongst others (….) infrastructure planning and design.

An archaeological dig to trace the background and development of a country’s standards might produce other pointers to a reduction in the number of design standards. Here for example is a quote from a document on the preparation of the “East African transport facilitation strategy” (ref. 311):

Geometric road design standards in Burundi  and Rwanda  are based on  the American standards while Kenya, Tanzania and Uganda are using their own standards which were developed largely from the American and English practice. (….) It should also be noted that countries like Tanzania has adopted some design  criteria  from  the  geometric  design  standard  of  the  Southern  African  Transport  and Communications  Commission  (SATCC),  which  was  also  derived  largely  from  the  American  and English practice.

More standards

However a country very often has more than one standard:

  • In the USA for example the AASHTO publications might be seen as “the” national standard, but (for example) there is also a Texas roadway design manual, documentation on Arizona roadway design guidelines (and so on).
  • In the UK there is a nationally valid “Design manual for roads and bridges”;  but the city of Leeds has a “Street design guide”,  and Lancashire county council has a document “Residential road design guide”….
  • Liverpool city council in Australia has its own geometric design standards (see here)

A country’s standards may change over time- for example, Malaysia has editions of its “Guide on the geometric design of roads” for 1986 and 2002; and Canada has issued separate documents as updates (e.g. the December 2011 Updates to the Geometric Design Guide for Canadian Roads). Further, regional standards may not necessarily replace all or even part of a country’s existing standard(s); they can even lead to an increase in the total number of standards.


One way to work towards a UHDS would be to begin by viewing highway design as the application of data from a series of modules. For example, a formula frequently used in highway curve design is

 Rmin = V2 / 127 (e+f)

Where Rmin = minimum horizontal radius

  • V = design speed in km/hr
  • e = elevation
  • F = coefficient of side friction

Here we could develop notes for the separate modules of : (the formula), e, f and perhaps V.

With road cross-sections, there could be separate modules for : (traffic) lane width, footpath, hard shoulder ….

We could begin to collect copies of highway design standards for different countries, and on a module -by-module basis (for example, side friction) extract the relevant information from each standard and see if they are the same, or if one or other represents a better practice. The hypothesis is that we would find very few unique, valid design standards for each module. The work could lead to a synthesis of material into just one or two options for each module.

At the moment there are scores of highway geometric standards. Where is the efficiency in publishing so many if they all say the same thing?


311 – Bureau for industrial cooperation, preparation of the East African Transport Facilitation strategy, thematic area 1, standards and specifications: Chapter 2, “Harmonisation of roadway geometric standards“.


About roadnotes

Robert Bartlett is an international consultant with over 30 years of professional experience as a highway and traffic engineer with leading companies and organisations in several countries, including Germany, China (Hong Kong), Qatar and the UK. Specialised in urban studies, transport and the use of GIS, research has included new ideas on subjects such as the study of social justice using GIS, the dimensions of vehicles, and comparative geometrics (highways and transport).
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