Why the street network speed matters
Street networks are all streets under the city's responsibility. The percentage of the street network at 20 mph or slower is a helpful measure for Vision Zero. Traffic speeds have a significant impact on how dangerous a crash is. Research from the American Automobile Association (AAA) Foundation for Traffic Safety shows that a pedestrian hit by a car going 20 mph has a 90% change of surviving the collision. If the car was going 30 mph, the change of survival goes down to 60%. Learn more about this research.
Across cities, when cars travel more slowly (20 mph or less), crashes involving pedestrians have a lower risk of severe injury.
Depending on the state, a city may have the ability to set its own default speed limit, or it may be limited by state regulations. A default speed is the usual speed across most of a city’s roads and is the speed any time a speed limit sign is not posted. Reviewing the default speed limit in addition to the percentage of streets under 20 mph allows us to understand the speed limits in a city.
Learn more about speed management in San Francisco.
Street network speeds
Data notes and sources
Data notes and sources
To report the street network data, we approached it in one of two ways. If a city reported the percentage of streets at 20 mph, we used that data. If that was not available, we found the miles of city streets at 20 mph and divided by the total miles of street. When the data was not available online, we reached out directly to peer cities to request it. The information was not available for all of our peer cities. Where publicly available, the links are below.
To report the default city speed, we researched into local city codes and state codes where applicable. Sources are linked below.
To view the full dataset, visit the DataSF Open Data Portal.
Key takeaways
The majority of cities have a default speed of 25 mph. Only Minneapolis, Portland, Seattle, and Washington DC have a default speed of 20 mph. Miami and Chicago have a default speed of 30 mph.
There is a large difference across cities in the percentage of streets at 20 mph. For Washington DC, Seattle, Portland, and Minneapolis, more than 60% of their streets have a speed limit of 20 mph. These cities have a default city of 20 mph, which means that unless otherwise posted the speed limit is 20 mph. The next closest are San Francisco and New York City, with between only 5-6% of the streets at 20 mph.
California legislation has a major impact on a city's ability to set speed limits. Until recently in California, state laws limited cities’ ability to change speed limits. Assembly Bill 43 (AB 43) came into effect in 2022, allowing cities to lower speeds by 5 mph in key business districts. In 2024, cities are now allowed to lower speeds by 5 mph in 'safety corridors'. Since AB 43's implementation, San Francisco reduced the speeds for 46 miles of streets as of April 2024. Learn more about this initiative.
Explore other metrics
Visit the Vision Zero Benchmarking home page to learn more about the effort and explore other metrics.