[BoulderCouncilHotline] Studies that show the safety benefits of reducing speed limits

[Brockett, Aaron]

Dear council and community members,

I wanted to share some scientific evidence to support our consideration of lowering the city speed limit to 20mph on local residential streets in advance of our public hearing Tuesday night.

Fundamentally, the reason to lower speeds is to reduce the risk of serious injury and crashes. This study from the AAA Foundation for Traffic Safety shows a clear correlation between higher speeds and an increased chance of serious injury and deaths for pedestrians. From the abstract: "Results show that the average risk of severe injury for a pedestrian struck by a vehicle reaches 10% at an impact speed of 16 mph, 25% at 23 mph, 50% at 31 mph..." and "These results could be used to inform efforts to improve pedestrian safety, for example, by limiting traffic speeds to levels that are unlikely to result in severe injury or death..." https://aaafoundation.org/impact-speed-pedestrians-risk-severe-injury-death/

Then the question is whether reducing the speed limit will actually result in lower driving speeds. Two studies that I've seen show that they do. In 2014, Bristol in the UK changed the speed limit to 20mph on local streets. A comprehensive study showed that the change reduced speeds by an average of 2.7mph -- "The findings indicate that the sign-only 20 mph intervention was successful in lowering individual vehicle speeds." https://www.sciencedirect.com/science/article/pii/S2214140518303141


Another study looked at the effectiveness of Boston, MA reducing their speed limit by 5mph and found that "Lowering the speed limit by 5 mph on city streets can improve safety for motorists, pedestrians and bicyclists alike by reducing speeding, new research by the Insurance Institute for Highway Safety indicates." https://www.iihs.org/news/detail/city-drivers-slow-down-for-lower-speed-limit-in-boston

So the evidence shows that reducing the speed limit will result in slower driving speeds, and therefore in reduced chances of serious injury or death for pedestrians, as well as cyclists.

Many thanks to Rebekah Dumouchelle, Ryan Welsh and Gary Sprung for bringing these studies to our attention, as well as to Community Cycles for their consistent advocacy on the issue. I look forward to our public hearing on the matter Tuesday night.

Best,

Aaron Brockett


 [cid:58ffc85d-040d-4e03-bb1c-42ca4db5cc19]

<http://www.bouldercolorado.gov/>

C: 720-984-1863

brocketta at bouldercolorado.gov

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