Seattle receives national recognition for preventing crashes with lower speed limits. Nearly half of Seattle’s major streets now have a 25 MPH speed limit.

Seattle saw dramatic reductions in crashes and injuries after installing 25 MPH speed limit signs, receiving recognition from national traffic safety officials.  

The National Association of City Transportation Officials (NACTO)– an organization which sets traffic safety guidance – released new recommendations which highlight Seattle’s safety achievements as a national best practice to prevent crashes and save lives. Seattle Department of Transportation (SDOT) has been making our streets safer by reducing speed limits to 25 MPH, and has released data showing that this reduced crashes by 22%.

“I’m thrilled that Seattle’s work to create a safer City for those walking, biking or rolling is being recognized nationally as a best practice and I hope more cities make critical speed changes to save lives. Even in a global pandemic, we must continue to make progress on our Vision Zero goals.”  

Mayor Durkan

This year we lowered speed limits on 90 miles of major streets, creating a total of over 200 miles of major roads with a 25 MPH speed limit. We’ll continue moving forward to lower speed limits on the rest of Seattle’s major streets over the coming year.

Map of Seattle showing that nearly half of Seattle’s major streets now have a 25 MPH speed limit

Mayor Jenny Durkan has championed lowering the speed limit on Seattle arterial streets to 25 MPH as one part of the plan to achieve our Vision Zero goal of ending traffic deaths and serious injuries on city streets by 2030. 

“Addressing dangerous speeding is the only way for everyone to get around safely. As we design a transportation network that serves everyone, we have to prioritize saving lives as we manage our streets.”

SDOT Director Sam Zimbabwe 

Seattle was one of the first cities in the country to study how reducing speed limits and increasing speed limit sign frequency improves safety. Since then, we’ve been actively implementing these changes across the city, improving safety for all who use our streets.

Graph showing planned speed limit reductions from 2015 to 2021

It is an established fact that slower speeds save lives. 

A person walking, rolling, or biking is twice as likely to be killed if they are hit by a person driving 30 MPH than someone going 25 MPH. 90% of people hit by cars going 20 MPH survive. 

Lowering speed limits has a negligible impact on how long it takes people to reach their destination and can actually reduce traffic congestion. It only takes 20-40 seconds longer to drive a mile at 25 MPH than at the previous speed limit. Meanwhile, about a quarter of the time we spend sitting in traffic is due to crashes which can often be prevented with lower speed limits.  

A person’s chance of surviving being hit by a car decreases drastically with faster speeds. Graphic: ProPublica. Data: AAA Foundation for Traffic Safety report.

But how do you get cars and trucks to slow down? 

Our Vision Zero plan involves many types of strategies, including engineering safer streets, educating and engaging the public about their role in travelling safety, and placing equity at the forefront of traffic safety. Within that framework, there are two main engineering mechanisms to how we design streets which lead to lower speeds and fewer crashes:

  • The presence and frequency of speed limit signs
  • Changes to the layout of streets in a way that encourages people to drive slower

Our study focused on reducing speed limits and increasing the frequency of speed limit signs. 

Map showing case study locations.

While we’ve been working to reduce speeding throughout Seattle, our new report is focused on a controlled study of streets in several North Seattle neighborhoods

We conducted a series of case studies along individual corridors and urban villages: 

  • Greenwood/Phinney Ave N
  • NW/N 85thSt
  • N/NE 45thSt
  • Greenlake/Roosevelt Urban Village
  • U-District Urban Center

In all these locations, we increased speed limit sign frequency to 4 signs per mile – over four times as many speed limit signs as there were before the study. Some of the locations did not previously have speed limit signs at all, and some locations were reduced from 30 MPH to 25 MPH. 

We specifically wanted to test the effectiveness of reducing speed limits and installing more signs closer together. In order to remove other variables from the experiment, we intentionally did not advertise the changes with a communications campaign, retime traffic signals, increase enforcement, or make any other engineering adjustments to the street design. 


Our study provided evidence that installing speed limit signs prevents crashes. We saw a 22% reduction in crashes and a 54% reduction in the most dangerous speeders. 

Chart showing crash data, including all crashes and injury crashes, before and after speed limit sign installation.

The median speed dropped by 10% and the number of people seriously dangerous speeders driving over 40 mph dropped by 54%. 


Seattle has shown that speed limit signs alone have a huge impact on public safety, even without changes in enforcement or urban design. 

Vision Zero sign that says "Look out for each other".

This finding is important because enforcement disproportionately impacts Black people and other people of color. At SDOT, we are learning and listening to how our urban spaces disproportionately place Black people in harm’s way. In addition, speed limit signs are the most cost-effective method of reducing speed, and lead to promising results for safety. 


Our local success in lowering speeds helped inform NACTO’s new 2020 speed limit recommendations. In addition, we’ve continued to lower speed limits and increase signage throughout Seattle. 

Elementary school parents and kids holding Vision Zero signs in 2017 encouraging people to slow down on Seattle streets.

In Seattle, this study helped informed Mayor Durkan’s decision to reduce speed limits across the city to 25 MPH as part of our plan to make our streets even safer & achieve our Vision Zero goal of ending traffic deaths & serious injuries on city streets by 2030. After seeing the success of our case studies, we’ve prioritized making streets safer in disadvantaged communities. 

Visit our Vision Zero webpage for more information about how we plan to end traffic deaths and serious injuries on city streets by 2030.