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Effects of city-wide 20 mph (30km/hour) speed limits on road injuries in Bristol, UK
  1. Anna Bornioli1,
  2. Isabelle Bray1,
  3. Paul Pilkington1,
  4. John Parkin2
  1. 1 Centre for Public Health and Wellbeing, Department of Health and Social Sciences, University of the West of England Bristol, Bristol, UK
  2. 2 Centre for Transport and Society, Department of Geography and Environmental Management, University of the West of England Bristol, Bristol, UK
  1. Correspondence to Dr Anna Bornioli, Health and Ssocial Sciences, University of the West of England Bristol, Bristol BS16 1QY, UK; anna.bornioli{at}


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.

  • speed
  • 20 mph limits
  • road injuries
  • longitudinal
  • stepped-wedge design

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  • Funding This study was supported by Bristol City Council.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.