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NACTO Releases City Limits, an Innovative Framework to Set Safe Speed Limits on City Streets

Jul 22, 2020

Over 35,000 people die on U.S. roadways every year, at a rate twice as high as peer countries
Current speed limit setting practice results in unsafe streets; new NACTO guidelines outline how to use a tested and proven safe systems approach to set safer speed limits in urban areas
Speeds and crash severity have increased on many streets during the coronavirus pandemic, underlining the importance of safer speed limits

For Immediate Release | July 22, 2020
Contact: Alex Engel | [email protected]
Guidance Available Online:

The National Association of City Transportation Officials (NACTO), today released an innovative, tested, and proven framework for setting safe speed limits for city streets. Developed by a steering committee of NACTO’s 86 member cities and transit agencies, City Limits outlines how to use a safe systems approach to set speed limits in urban environments, in contrast to legacy methods (e.g. the 85th percentile) that often result in speeds that are inappropriately fast for urban environments.

City Limits outlines a three-method approach to speed limit setting that provides an alternative to percentile-based speed limit setting:

  1. Setting default speed limits on many streets at once (such as 25 mph on all major streets and 20 mph on all minor streets),
  2. Designating slow zones in sensitive areas, and
  3. Setting corridor speed limits on high priority major streets, using a safe speed study, which uses conflict density and activity level to set context-appropriate speed limits.

The methods outlined in City Limits can be combined, and, unlike percentile-based approaches, each is context-sensitive, allowing cities to holistically evaluate who is using streets and how people are using them, from people walking and biking, to those taking transit or visiting a school. The guidance ranges from step-by-step checklists for conducting activity level & conflict density analyses, to nuanced metrics for documenting speeds that go beyond percentile-based speed setting practices.

Over 35,000 people die on US roads every year, a traffic safety crisis unmatched in severity by the US’s industrialized peers. Speed is what most often turns a crash deadly. A person hit by a car traveling at 35 miles per hour is five times more likely to die than a person hit at 20 miles per hour. Yet, speed limits in the US are often set in a process that largely ignores anyone outside of a car.

“Most speeds limits are set using an oversimplified and outdated method: measure 100 drivers traveling without any traffic and set the speed limit based on the 15th-fastest driver,” said Jenny O’Connell, NACTO Program Manager. “If this sounds like a system that would create dangerous outcomes, that’s because it does. Even worse, in many cases, speeds ramp up over time as drivers respond to speed limit signs and speed a few miles per hour over the posted limit, creating a negative feedback loop of faster, less safe streets.”

In many areas, cities rely on police enforcement to compensate for a lack of flexibility in engineering and speed limit setting policies, a practice that is not proven to reduce traffic injuries or fatalities and often increases risk for Black people and other people of color on city streets. A growing body of evidence shows that speed limit changes alone can lead to measurable declines in speeds and crashes, even absent enforcement or engineering changes.

The importance of safe speed limit setting has been underscored in recent months by effects from the coronavirus pandemic. As people traveled less during stay-at-home orders, speeds increased to even more unsafe levels. In May, traffic across the U.S. was 41% lower than pre-pandemic volumes, yet crashes only dropped 21%, meaning each trip was riskier.

“Context-sensitive speed limit setting means that safe speeds are chosen based on how a street is used, and the important functions it plays in a community,” said Corinne Kisner, NACTO Executive Director. “An increasing number of cities are moving beyond the flawed assumptions in the 85th percentile approach, and have developed new ways to set speed limits. We’re proud to have worked with these cities to document and codify these groundbreaking approaches, which have already saved many lives, and have the potential to save thousands more every year.”

“Slower is safer. In Minneapolis, we are lowering our residential speed limit to 20 mph, and our major streets to 25 mph because we know it will save lives,” said Robin Hutcheson, Minneapolis Director of Public Works and NACTO President. “NACTO’s new guidance will help cities across the country use a modern, adaptive approach to speed limit setting that centers safety—not speed—as the primary goal. City Limits reflects intense effort from city staff who are doing the work every day, and provides expert guidance for cities to prioritize the safety of people traveling, especially our most vulnerable users.”

“Among New York City’s very first Vision Zero accomplishments in 2014 were persuading our State Legislature to allow us to lower our default speed limit to from 30 mph to 25 mph and to expand our automated enforcement program. Both have been central to the progress we have made since then in reducing fatalities,” said New York City Transportation Commissioner Polly Trottenberg. “Speed management is the number one priority in roadway safety. Vehicles traveling at safer speeds are far less likely to be involved in fatal crashes. I thank the team at NACTO for providing the detailed guidance of City Limits, an invaluable resource on how to achieve safer speed limits—and save lives on our nation’s streets.”

“The City of Atlanta is excited about the release of NACTO’s speed limit setting guidance,” said Josh Rowan, Commissioner of the Atlanta Department of Transportation. “We recently adopted Vision Zero and legislated a default 25 MPH speed limit on certain city-controlled streets. This guidance has been and will continue to be beneficial in establishing safe speed limits on our urban arterial streets that feel and function like suburban roads, where using the traditional 85th percentile methodology will only lead to higher speed limits being set. NACTO continues to be a leader in urban street design and forges the way for many cities like us to create safer streets and move closer to realizing zero fatalities.”

“As vehicle speeds increase above 15 mph, crashes quickly get deadly. If you’re hit by a car at 15 mph, you’ll likely recover. At 45 mph, you’re dead. Reducing speeds is a critical step to saving lives,” said Jeffrey Tumlin, Director of Transportation, San Francisco Municipal Transportation Agency (SFMTA). “NACTO has elevated the importance of this necessary strategy. In California, we continue to pursue legislative action for setting rational speed limits. NACTO’s guidance provides national leadership on this critical issue.”

“The traditional method of setting speed limits based on the 85th percentile ignores many realities of cities, particularly the connection to nearby land uses,” said Joseph Barr, Cambridge Director of Traffic, Parking, and Transportation and NACTO Board Member. “We’re thrilled to support City Limits, which outlines methodologies for setting speeds that put the safety of people front and center. This guidance will help cities move from a percentile-based system that rewards unsafe speeding towards one that helps achieve a safer environment for everyone using city streets.”

“Traditional transportation design has focused on designing streets and roadways for speeds that are generally inappropriate, especially in an urban context, contributing to unnecessary loss of life and serious injuries,” said Billy Hattaway, Transportation Director, City of Orlando. “Practitioners need guidance on reducing posted speeds and managing speed to improve safety for all users, especially vulnerable users such as pedestrians and bicyclists. This is an essential guide to support that goal.”

“A safe street is not one where safety is determined by how fast someone can comfortably drive, but rather one where a person can comfortably walk, ride a bike, and cross the street using a wheelchair,” said Ryan Noles, Senior Transportation Planner, City of Boulder. “City Limits creates a framework to move beyond setting speed limits using the 85th percentile, to a place where cities can set speed limits that prioritize policy goals. Boulder is proud to have already adopted a 20 mph default speed limit across the city, and going forward we will be working to meet the intent of that policy and make our streets slower, and safer, for everyone.”

“It’s crucial that cities inform and inspire each other as we work towards Vision Zero,” said Chris Warner, Transportation Director for the City of Portland, Oregon. “I’m proud to work with cities that collaborate and bring the nation’s best ideas to their local communities. In Portland, we reduced the speed limit on most city streets to 20 mph in Portland with broad public support. By working together, we can save lives, while making our cities more vibrant and sustainable.”

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

“From 2010 to 2019, most Washingtonians killed while walking or biking (87%) died on roads with a posted speed of 30 mph or higher. To tackle this critical problem, WSDOT is leading a multi-agency, multidisciplinary group working on a model policy addressing speed management for injury minimization,” said Keith Metcalf, Deputy Secretary, Washington State Department of Transportation. “We know we need to apply design tools and create ‘self-enforcing’ streets that help drivers move at speeds appropriate to the context. We want to be a partner with our cities and counties in saving lives, and City Limits will help us work with them.”

“Thank you to NACTO for publishing this guide, and elevating the significant relationship between speed and safety for all road users,” said Stephanie Pollack, Secretary and CEO, Massachusetts Department of Transportation. “This guidance comes at an especially important time as the rate of fatal crashes has increased during COVID and we need safer speeds to prevent serious injuries and fatalities.”

“ITE congratulates NACTO on the development and publication of this important new speed management resource,” said Jeff Paniati, Executive Director and CEO of ITE. “Determining and achieving context-appropriate target speeds on urban streets is essential to the vision of zero fatalities and serious injuries.”

“The top priority in our nation’s transportation policy and program is to let vehicles go fast. It has filtered into every level of implementation, down to the way we set speed limits. We raise the speed limit to suit the speeders, as long as there are enough of them (and it doesn’t take that many),” said Beth Osborne, Director of Transportation for America. “NACTO once again provides excellent guidance to practitioners who recognize the problem and who want to put safety ahead of speed.”

“The soaring number of pedestrian deaths we’ve seen in recent years is a wake-up call for a new approach to vehicle speeds in urban areas,” said Jessica Cicchino, Vice President for Research at the Insurance Institute for Highway Safety (IIHS). “IIHS research demonstrates that lowering city speed limits curbs the most dangerous speeding and can make the roads safer for everyone who drives, walks, or bikes.”

“To advance Vision Zero, nothing is more important than managing speeds,” said Leah Shahum, Founder & Director, Vision Zero Network. “For too long, cities have been hindered from setting speeds to promote safe mobility for all. This resource will help usher in a new day of safety on our streets, especially our most vulnerable—children, seniors, and people walking and biking.”

City Limits is available as a free resource at

About the National Association of City Transportation Officials (NACTO)
NACTO is an association of 86 major North American cities and transit agencies formed to exchange transportation ideas, insights, and practices and cooperatively approach national transportation issues. The organization’s mission is to build cities as places for people, with safe, sustainable, accessible, and equitable transportation choices that support a strong economy and vibrant quality of life. To learn more, visit or follow us on Twitter at @NACTO.