Skip to Content
Streetsblog USA home
Streetsblog USA home
Log In
Safety

Compelling Evidence That Wider Lanes Make City Streets More Dangerous

The rate of side impact crashes is lowest on urban streets with lanes about 10.5 feet wide -- much narrower than the standard 12 feet. Graph: Dewan Karim
The safest lane width is narrow, but not too narrow. Graph: Academia.edu

The "forgiving highway" approach to traffic engineering holds that wider is safer when it comes to street design. After decades of adherence to these standards, American cities are now criss-crossed by streets with 12-foot wide lanes. As Walkable City author Jeff Speck argued in CityLab last year, this is actually terrible for public safety and the pedestrian environment.

A new study reinforces the argument that cities need to reconsider lane widths and redesign streets accordingly. In a paper to be presented at the Canadian Institute of Traffic Engineers annual conference, author Dewan Masud Karim presents hard evidence that wider lanes increase risk on city streets.

Karim conducted a wide-ranging review of existing research as well as an examination of crash databases in two cities, taking into consideration 190 randomly selected intersections in Tokyo and 70 in Toronto.

Looking at the crash databases, Karim found that collision rates escalate as lane widths exceed about 10.5 feet.

Roads with the widest lanes -- 12 feet or wider -- were associated with greater crash rates and higher impact speeds. Karim also found that crash rates rise as lanes become narrower than about 10 feet, though this does not take impact speeds and crash severity into account. He concluded that there is a sweet spot for lane widths on city streets, between about 10 and 10.5 feet.

In Toronto, where traffic lanes are typically wider than in Tokyo, the average crash impact speed is also 34 percent higher, Karim found, suggesting that wider lanes not only result in more crashes but in more severe crashes.

The "inevitable statistical outcome" of the "wider-is-safer approach is loss of precious life, particularly by vulnerable citizens," Karim concluded.

Stay in touch

Sign up for our free newsletter

More from Streetsblog USA

Spooky Stuff: On Halloween, Some States Will Have Deadlier Roads Than Others

Find out how yours ranks — and what policymakers can do to make streets less scary.

October 30, 2025

Who Are Thursday’s Headlines For?

Non-drivers still perceive streets as being for cars even when they have bike lanes. And that's because, in many cases, they are.

October 30, 2025

An Olympian Task: Replicating Paris’s Bike Boom in Los Angeles

The Olympics can help transform the streets of Los Angeles  — if they look to the example of Paris.

October 29, 2025

Wednesday’s Headlines Are a Clear and Present Danger

Rescinding the "endangerment finding" could not only exacerbate climate change, it could also throw entire industries into chaos.

October 29, 2025

What’s More Regressive: Modest Driving Surcharges to Help Fund Transit, or Forced Car Ownership?

Do Illinois state senators and reps really want to make the financial burden on their constituents less "regressive"? If so they can start by ensuring that as many people as possible can live their lives without spending $12,000 annually just to leave their homes.

October 28, 2025

Tuesday’s Headlines Pay High Prices for Highway Repairs

If the U.S. didn't spend so much money on repaving roads, there might be more left over for other things, like transit.

October 28, 2025
See all posts