Study: Seattle’s Lower Speed Limits Reduced Crash Injuries

A change in the city’s speed limits has been shown to reduce the likelihood of injuries during collisions.

1 minute read

March 30, 2023, 11:00 AM PDT

By Diana Ionescu @aworkoffiction


25 mph speed limit sign partially obscured by red and orange fall leaves

Dmitri Kotchetov / 25 mph speed limit sign

A new study from the Insurance Institute for Highway Safety (IIHS) reveals that lowering speed limits on Seattle streets, part of the ‘Safe System’ approach that prioritizes road design and policies that limit the damage caused by human error, improved safety. “In downtown Seattle, lowering default speed limits reduced the likelihood that a crash would involve an injury by a fifth on arterial roads, IIHS researchers found. Outside of the city center, where the new limits were less consistently implemented and publicized, there were smaller injury reductions, but these were not statistically significant.”

The study credits the success in part to the city’s information campaign. “To make drivers aware of the change, the city conducted a public outreach campaign and installed gateway signs indicating the new citywide limits on arterial roads into the city, highway off-ramps and ferry terminals,” and installed new 25 mph signs on downtown arterials.

The study is the first to attempt to quantify the effect of lower speed limits on injury rates, not just on peeding. As the press release explains, “Higher speeds make crashes more likely by reducing the time a driver has to react and increasing the distance required to stop the vehicle. Higher speeds also increase the energy involved in a crash, raising the odds of an injury.”

Tuesday, March 28, 2023 in Insurance Institute for Highway Safety

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.

June 25, 2025 - Diana Ionescu

Map of Western U.S. indicating public lands that would be for sale under a Senate plan in yellow and green.

Map: Where Senate Republicans Want to Sell Your Public Lands

For public land advocates, the Senate Republicans’ proposal to sell millions of acres of public land in the West is “the biggest fight of their careers.”

June 19, 2025 - Outdoor Life

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

Close-up of full beer glass with purple train-themed design sitting on bar between two frosty tall cans.

Platform Pilsner: Vancouver Transit Agency Releases... a Beer?

TransLink will receive a portion of every sale of the four-pack.

June 30 - Cities Today

Vintage red Toronto streetcar passing in front of Rogers Arena in Toronto, Canada.

Toronto Weighs Cheaper Transit, Parking Hikes for Major Events

Special event rates would take effect during large festivals, sports games and concerts to ‘discourage driving, manage congestion and free up space for transit.”

June 30 - blogTO

Map of Berlin with ring roads in green and red.

Berlin to Consider Car-Free Zone Larger Than Manhattan

The area bound by the 22-mile Ringbahn would still allow 12 uses of a private automobile per year per person, and several other exemptions.

June 30 - Streetsblog USA

Urban Design for Planners 1: Software Tools

This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.

Planning for Universal Design

Learn the tools for implementing Universal Design in planning regulations.