We’re big fans of the Essential Evidence series of one page summaries of peer-reviewed literature on current transport policies and practice. This is produced by Bristol based Dr Adrian Davis in order to ensure that academic research and evidence informs implementation of planning and policy. Although sadly one recent summary shows that politicians are far more resistant to this than professionals and communities (No 187: Examining the politics of transport planning).

Summary No 185 is another confirmation of the robustness and effectiveness of the city-wide Bristol scheme, The effectiveness of a 20mph speed limit intervention on vehicle speeds in Bristol. Key points include:

  • Prior research has confirmed that there is a 6% reduction in collisions with each 1mph reduction in average speed
  • Reduction of individual vehicle speeds on those roads which received the intervention was 2.66 mph
  • Compliance to the posted speed limit improved following the intervention in both 20 mph and 30 mph roads