Width of a traffic lane / hypothesis

The Oxford Dictionaries say that a hypothesis is “a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation”. A review of the literature shows dozens of possible values for lane width for motor vehicles. (see for example here).My hypothesis is that there need only be seven possible values for these lane widths, and that these values can be related to other parameters such as speed (for example, as shown in the figure below).lane width 4_1

The figure shows 7 suggested lane widths and a possible relationship with speed

These lane widths appear in standard road cross-sections shown in the new German highway design standards, for example in the RAA and the RASt 06 (refs. 1615 and 1920). The same concept (step changes of 0.25m around a base figure of 3.00m) also apparently in Japan highway design standards (see e.g. table 2 in ref. 1719), the Georgia design standards (ref. 1389 attachment 4), the Albanian standards (ref. 1155 table 3.4), the ASEAN standards (ref. 1884).

Country standards with lane widths which do not conform with the above values include Nigeria (widths include 3.65m and 4.25m (ref. 1505) and the USA. The USA’s AASHTO green book (ref.831) says that “Lane widths of 2.7 to 3.6 m [9 to 12 ft] are generally used, with a 3.6-m [12-ft] lane predominant on most high-speed, high-volume highways”.


I was going to argue that exceptions to these 7 widths could be allowed in an existing built-up environment, where road improvements should arguably be a spin-off between urban architects, landscape architects and highway engineers. However probably this would be wrong, as consistency in design (and so here, in lane widths) should help increase road safety.


831 – USA, “A policy on the geometric design of highways and streets “, AASHTO, 2011

1155 – Albania, “ARDM 2 Road design manual vol. 2 / geometric Design”, MPWTT, 2007

1389 – Georgia, “SST Gzebi:2009 / Georgia road design standards”, LEPL National Agency for Standards, 2009

1505 – Nigeria, “Highway manual part 1 Design / vol. I: geometric design”, Federal Ministry of Works, 2013

1615 – Germany, “RAA Richtlinien für die Anlage von Autobahnen“, fgsv, 2010

1719 – Japan, Ohnishi et al, “Recent developments of road geometric design in Japan”, 3rd InternationalSymposiumon Highway Geometric Design, 2005

1884 – ASEAN, “ASEAN highway standards”, 2003

1920 – Germany, “Richtlinien für die Anlage von Stadtstraßen“, fgsv, 2006


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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