Width of a traffic lane (2)

In a recent blog post (here) I wrote that “one of the main elements of a road cross section are the traffic lanes – indeed, the traffic lanes are the only reason the road exists. After a century or so of developing roads you would expect there to be some sound practical concept for deciding what the width of these traffic lanes should be”.

I suggested that three approaches could be considered, and wrote briefly about the first one, “lane width based on figures from history”. For example, a brief look at different editions of the AASHTO Green Book gives the idea that over perhaps 50 years or so this source has consistently indicated lane widths of 2.7 to 3.6 m, with a 3.6m lane “predominant on most high-speed, high-volume highways”

A second approach to deciding on the width of a traffic lane would be to check existing standards and guidelines. I made a brief and not-exhaustive trawl through some road design guidelines and developed the table below (note that the figures are all for straight roads). More work would likely produce a table with suggested traffic lane widths for at least every 10 cm increase in width, from say 1.0 m to 4.5m and above

Discussion

I have a feeling something is not plausible here. For example, road widths are a committment over some 20 years or more, whilst vehicle dimensions (perhaps) change with time, and transport policies – such as more bike lanes – certainly change with time. Also in theory, perhaps highway engineers and drivers should expect to find the same lane widths in similar circumstances, whichever country they happened to be driving in. The table with its many different values gives the impression of design overkill. It might be that a more limited number of recommended values for traffic lane width would be a good idea.

lane width 2

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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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