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Setting Safer Speed Limits

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Reducing speed limits can be an effective tool for reducing speeds, crashes, and serious injuries and deaths, even absent other design or enforcement changes.

High vehicle speed increases both the likelihood and severity of a crash, because it diminishes drivers’ ability to recognize and avoid potential conflicts. On streets with higher speed limits, traffic engineers also have fewer design options to increase safety. Speed limit reductions can also be an important communications tool; by lowering the permitted speed on a street, cities communicate that they know lower speeds are more appropriate for places where people live.

City transportation agencies have long understood that vehicle speed plays a key role in fatal and serious crashes, and have sought to reduce speeds through design and regulation. But speed limit reductions have remained out of bounds for many cities because authority over speed limits is often held at the state level, and is commonly tethered to the practice of using the existing speeds on a street to determine what the speed limit should be. This flawed model uses current driver behavior to determine speed limits, instead of allowing engineers and planners to set the limit that will create the best, safest conditions for road users. The result is higher speeds and speed limits over time.

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City Limits

In 2020, NACTO published City Limits, the first-ever speed limit setting guidance that places safety as the top transportation priority. The guidance recommends using a context-sensitive approach to set speed limits in line with the maximum safe speed that drivers should be traveling on a given road, rather than based on how fast they are already traveling.

Recognizing that city authority to set speed limits varies by jurisdiction, City Limits offers three tools for setting speed limits on urban streets:

  • Setting default speed limits on many streets at once.
  • Designating slow zones in sensitive areas.
  • Setting corridor speed limits on high-priority streets using a Safe Speed Study.

City Limits maps a new path for US cities, codifying speed limit setting best practices that have been tested and documented in cities across North America. Cities can create better and safer outcomes for all by adopting these speed limit setting practices as part of their traffic fatality reduction or Vision Zero programs. By managing speeds, cities can save lives.

Experience from other industrialized countries shows that fewer traffic deaths and safer roads are possible. City Limits encourages transportation leaders to take a Safe Systems approach focused on changing the policies and engineering decisions that create unsafe street conditions, rather than focusing on the behavior of individual road users.

Read the full report. >


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Where are Speed Limits Changing?

Between 2020 and 2023, at least 22 cities in the U.S. and Canada have reduced speed limits on some or all streets. These cities join a handful of others that undertook major speed limit changes prior to 2020. We’ve mapped out these efforts below.

NACTO continues to push for changes to speed limit policies, and to track changes as they occur cross to the country. Want to add your city to our map? Fill out this Google Form.