This is part five in our series on Building Safer Streets. Find an overview and other parts of the series here.
The way we design roads dictates the speeds that drivers adopt, regardless of the posted speed limit. Safe Systems research demonstrates that visual cues from the roadway ahead directly influence how drivers operate vehicles, effectively bypassing the brain.
A surprisingly effective visual cue is just to narrow the travel lanes. It may seem that wide lanes may seem like they are safer because they reduce the risk of vehicles drifting out of lanes and causing collisions. While that may make sense on high speed freeways, traffic engineers have mandated wide lanes to many arterial and residential streets with dangerous consequences. Indeed, excessively wide lanes are one reason why multi-lane arterials are the most dangerous road type.
Here’s why it matters. Research has demonstrated that wide straight travel lanes with long sight lines induce high travel speeds. Those speeds can be deadly in the complex environment of cities and towns, which involve driveways, turning vehicles, and most importantly, people using the streets as pedestrians.
Check out this chart which demonstrates the connection between lane width and travel speeds.
A growing movement over the last two decades has worked to reform traffic engineering practices and to highlight the dangers of excessively wide lanes. The National Association of City Traffic Officials lays out clear recommendations in a design guide on lane width, which we quote here in full:
- Lane widths of 10 feet are appropriate in urban areas and have a positive impact on a street’s safety without impacting traffic operations.
- For designated truck or transit routes, one travel lane of 11 feet may be used in each direction. In select cases, narrower travel lanes (9–9.5 feet) can be effective as through lanes in conjunction with a turn lane.
- Lanes greater than 11 feet should not be used, as they may cause unintended speeding and assume valuable right-of-way at the expense of other modes.
- Restrictive policies that favor the use of wider travel lanes have no place in constrained urban settings, where every foot counts. Research has shown that narrower lane widths can effectively manage speeds without decreasing safety and that wider lanes do not correlate to safer streets. Moreover, wider travel lanes also increase exposure and crossing distance for pedestrians at inter-sections and midblock crossings.
It’s fascinating that just putting the painted lines closer together can have such a positive impact on speed.
So next time you are advocating for a safer street, ask your local official “what are the lane widths?” If they are too wide, ask why your officials are bringing dangerous highway style design into your community, and share this post and the above recommendations from NACTO.
