Bristol’s 20mph limits have led to valuable reductions in speed and casualties, and benefit active travel

The University of the West of England (UWE) has analysed the impact of 20mph roll-outs for Bristol City Council. It finds reductions of 2.7mph in average traffic speeds and an estimated cost saving of over £15m per year from fatal, serious and slight injuries avoided.

The research[1] took a holistic, public health approach to evaluation, using a variety of data sources to examine changes in vehicle speeds, road traffic casualties, levels of walking and cycling, public perceptions and attitudes, and reported levels of health and wellbeing across the communities in Bristol before and after the introduction of 20mph speed limits across Bristol.

Key findings were :-

  • Statistically significant reductions in average traffic speeds of 2.7mph across the city of Bristol, following the introduction of 20mph speed limits. This is a larger reduction than seen in previous evaluations in other cities.
  • The study employed a more sophisticated analysis than previous studies of 20mph limits, including using individual speed data from over 36 million vehicle observations and controlling for other factors that might affect changes in traffic speeds.
  • There has been a reduction in the number of fatal, serious and slight injuries from road traffic collisions. Casualties avoided per year are 4.53 fatalities, 11.3 serious injuries and 159.3 slight injuries.
  • These equate to an estimated cost savings of over £15 million per year. This is an annual savings over 5 times greater than the one-off implementation cost of £2.77m.
  • Although there is still majority support for 20mph speed limits in Bristol, there remains concern about compliance and behaviour of other drivers.
  • Walking and cycling across Bristol has increased, both among children travelling to school and adults travelling to work.
  • The introduction of 20mph speed limits in Bristol offers a model for other towns and cities across the UK, who are seeking to reduce traffic speeds, cut road traffic casualties, and promote community health and well-being through road danger reduction.
  • In order to assess effectiveness of 20mph speed limits, it is vital that other towns and cities follow Bristol’s example, and prioritise the ongoing collection and analysis of appropriate data on vehicle speeds, road traffic casualties and wider public health impacts.

Rod King MBE, Founder and Campaign Director for 20’s Plenty for Us commented :

“This report builds on the findings of other 20mph cities and towns. Default 20mph limits are an important foundation for making our places better places to be. They are affordable, reduce speeds, reduce casualties and make our places more friendly for walking and cycling. This study shows that the public health benefits are significant. It is now time to standardise on a 20mph default at national level to increase benefits, reduce implementation costs and maximise the excellent return on public funds.”

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[1] The Bristol Twenty Miles Per Hour Limit Evaluation (BRITE) Study -Pilkington, P., Bornioli, A., Bray, I. and Bird, E. (2018) -

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