Safer urban car lane widths

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Readers need to be aware that this post does have a bias toward giving weaker road users a higher priority for road space. My reading of these design manuals is therefore to identify the widths providing greatest benefit for people aged 8 to 80.
First warning: For this post, lane width is about the distance between painted lines or changes in road surface texture. Kerbs/road bumps greater then 50mm in height limit the available options. See the photo at the end of this post.

New Zealand legislation states that a “lane for the use of vehicular traffic … is at least 2.5 m wide” Reprinted 1 October 2017 – Land Transport (Road User) Rule 2004 (SR 2004/427)

Here is an example (in Schiedam) of narrowed motor vehicle lanes with the cycle lane width being maintained through the intersection. As we can all see, this doesn’t mean excluding heavy traffic (note bus stop). What it does mean is that the safety* a cycle lane width gives can be continued through the intersection.

*“Cycle lanes … provide a modest 10% safety improvement for cyclists, but 30% for pedestrians” This is from the NZTA Pedestrian planning and design guide Table 6.3

Data collected from the Minneapolis-St. Paul and Oakland County – Detroit areas does not support the idea of wider lanes being safer for motorists.

“There is no indication that the use of 3.0- or 3.3-m (10- or 11-ft lanes), rather than 3.6-m (12-ft) lanes, for arterial midblock segments (& arterial intersection approaches) leads to increases in accident frequency.” P23 (P25)

Ref: Relationship of Lane Width to Safety for Urban and Suburban Arterials – 2007 by Ingrid B. Potts, Douglas W. Harwood, and Karen R. Richard

Measures from Tokyo & Toronto also do not support wider lanes being more efficient for motorists. Ref: Narrower Lanes, Safer Streets – Dewan Masud Karim – 2015

Impact on Traffic Capacity and Congestion:

“Contrary to common belief, the results clearly demonstrate that narrower travel lanes, particularly 3.0m lanes, carry the highest traffic volumes (18% higher compared to 3.5m lane) … there is no measurable decrease in urban street capacity when through lane widths are narrowed from 3.7m to 3.0m … Traffic delays on urban roads are principally determined by junctions, not by midblock free flow speeds” p12

Large Vehicles and Narrower Lanes:

“Low volume trucks (less than 5%) experience no operational problems for narrower lane widths … For buses, it suggests using 3.3m for mixed traffic conditions and 3.0m where buffered bicycles lanes exist” p13

Lane widths to avoid – From Handbook for cycle-friendly design by UK based Sustrans 

“Avoid widths between 3.1 and 3.9m” p17

“Bus lanes widths … 3.2m to 3.9m to be avoided” p19

In my opinion it is particularly important that when narrowing lanes that kerbs and speed bumps are kept as low as possible. People stop for a variety of reasons. Bumps can make the ride in a bus uncomfortable or an ambulance trip worse than it needs to be.

Photo Gottingen – Lange Geismar Str

Past Blog post on lanes

A good one way cycle lane width = 2m+

4 lane roads when to

Lane width and cars per hour per lane

Number of cars per lane

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