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Effects of city-wide 20 mph (30km/hour) speed limits on road injuries in Bristol, UK

Bornioli, Anna; Bray, Isabelle; Pilkington, Paul; Parkin, John


Issy Bray
Associate Head of Department, Research and Knowledge Exchange

John Parkin
Professor in Transport Engineering


Twenty miles per hour (32 km/hour) or 30 km/hour speed limits represent a potential strategy to reduce urban road injuries and are becoming increasingly widespread. However, no study has conducted a robust evaluation of the effects of city-wide 20 mph speed limits on road injuries. This study reports the effects of such an intervention, based on a natural experiment that took place in Bristol, UK. Based on a stepped-wedge design using count data, negative binomial regressions showed that between 2008 and 2016, the 20 mph speed limit intervention was associated with a city-level reduction of fatal injuries of around 63% (95% CI 2% to 86%), controlling for trends over time and areas. There was also a general trend of reduction of the total number of injuries at city level and in 20 mph roads. These findings highlight the potential benefits of city-wide 20 mph speed limits. We hypothesise that this city-wide approach may encourage a general behaviour change in drivers that, in turn, may contribute to reducing injuries across the city.


Bornioli, A., Bray, I., Pilkington, P., & Parkin, J. (2020). Effects of city-wide 20 mph (30km/hour) speed limits on road injuries in Bristol, UK. Injury Prevention, 26(1), 85-88.

Journal Article Type Article
Acceptance Date Jun 26, 2019
Online Publication Date Jul 13, 2019
Publication Date Feb 1, 2020
Journal Injury Prevention
Print ISSN 1353-8047
Electronic ISSN 1475-5785
Publisher BMJ Publishing Group
Peer Reviewed Peer Reviewed
Volume 26
Issue 1
Pages 85-88
Keywords speed, planning, public health, motor vehicle, longitudinal methodology
Public URL
Additional Information This article has been accepted for publication in Injury Prevention, 2019 following peer review, and the Version of Record can be accessed online at:


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