Narrower Lanes, Safer Streets

A new study indicates that the safest urban streets have lanes that measure 10-10.5 feet wide. Narrower and wider lanes have higher crash frequencies, and wider lanes have higher crash severity.

2 minute read

June 2, 2015, 7:00 AM PDT

By Todd Litman


End of the rainbow

Clemens v. Vogelsang / Flickr

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 a column last year, this is actually terrible for public safety and the pedestrian environment.

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.

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

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.

Wednesday, May 27, 2015 in Streetsblog USA

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Cover CM Credits, Earn Certificates, Push Your Career Forward

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

July 2, 2025 - Diana Ionescu

Aerial view of town of Wailuku in Maui, Hawaii with mountains in background against cloudy sunset sky.

Maui's Vacation Rental Debate Turns Ugly

Verbal attacks, misinformation campaigns and fistfights plague a high-stakes debate to convert thousands of vacation rentals into long-term housing.

July 1, 2025 - Honolulu Civil Beat

Person wearing mask walking through temporary outdoor dining setup lined with bistro lights at dusk in New York City.

Restaurant Patios Were a Pandemic Win — Why Were They so Hard to Keep?

Social distancing requirements and changes in travel patterns prompted cities to pilot new uses for street and sidewalk space. Then it got complicated.

June 19, 2025 - Diana Ionescu

Aerial view of new neifhborhood under construction with enpty lots in foreground.

In California Battle of Housing vs. Environment, Housing Just Won

A new state law significantly limits the power of CEQA, an environmental review law that served as a powerful tool for blocking new development.

July 2 - CALmatters

Low-rise Pearl Sreet mall in Boulfer, Colorado.

Boulder Eliminates Parking Minimums Citywide

Officials estimate the cost of building a single underground parking space at up to $100,000.

July 2 - Boulder Reporting Lab

Two-story buildings with porches in walkable Florida neighborhood.

Orange County, Florida Adopts Largest US “Sprawl Repair” Code

The ‘Orange Code’ seeks to rectify decades of sprawl-inducing, car-oriented development.

July 2 - CNU Public Square