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).
This entry was posted in comparative geometrics, highway design standards and tagged , . Bookmark the permalink.

3 Responses to Width of a traffic lane (2)

  1. Sean Jones says:

    I am unsure whether you are still active, but thank you for our blog. I am seeking information about the width of single lane two-way roads in the UK, specifically whether there is a European or UK standard or minimum width. Briefly, there is a pinch point in an A-road close to my home where two HGVs heading in opposite directions are unable to pass without one giving way. Alongside the pinch point are pedestrian pavements edged by Grade 2 listed dwellings. The pavements are exceedingly narrow and pedestrians are endangered by vehicles necessarily driving on to the pavement to avoid oncoming traffic because the road is too narrow. I would be most grateful of you could point me in the direction of best practice guidelines or regulations about the minimum width of A-roads?

  2. Denny Murphy says:

    Thanks for the info. I don’t think the range in different widths is design overkill although there is probably some of that. Road widths often vary due to environmental changes, sight-lines and terrain.
    For example areas that have snow and ice provide some extra width as a place to pile snow and as a safety precaution. Also the snow plows are wider than an average vehicle. Areas with hurricanes have high crowns in the center of the road and narrower width lanes to shed 8″ of rain per hour by design. Thank you for the comparative research, it is useful for us architects and engineers.

    • roadnotes says:

      Thanks for your comments. I certainly found your comment about hurricanes and high crowns very interesting. Maybe the same design principle should apply to roads in the tropics? Your other comments made me think that, maybe a range of road widths is not a bad idea BUT there should be some explanation for the different widths (such as those you quote), and that the same range should apply in every country.

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