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UK researchers show 20mph zones effective in reducing road casualties

A review of published evidence by a team of researchers in the UK has found 20mph zones to be effective in reducing the number and severity of traffic collisions and casualties.

The research, published in the Journal of Transport and Health provides important evidence to support the implementation of 20mph speed zones across the UK and Europe.

The research, funded by the National Institute for Health Research (NIHR), is part of the largest and most comprehensive study to date into the effects of 20mph speed limits and speed zones to be undertaken in the UK.

Speed limits typically involve legislation and road signage whereas speed ‘zones’ also involve the use of physical traffic calming measures such as road narrowing and speed humps.

Road traffic injuries are a leading cause of preventable death globally. According to the WHO, the tenth leading cause of death worldwide is a result of road injury.

The primary reason for the introduction of interventions to reduce traffic speed is to lessen the likelihood of a collision occurring, and to reduce the severity of road traffic casualties.

Our findings show a growing body of evidence to support the use of 20mph zones, showing them to be effective in reducing the number and severity of collisions and casualties. Our research also found an increase in participants walking and children cycling spontaneously in 20mph zones, indicating the potential indirect positive impact on physical activity.

While our research has shown a number of benefits of 20mph speed zones, it has also highlighted a lack of current evidence relating to the impact on public health, air pollution, and noise pollution. Further evidence is also required around the effectiveness of signage-based speed limits. We need to continue to gather and build on this evidence so that we can adequately inform future road safety policies that could help to address the global epidemic around road injuries.

—Dr Ruth Hunter, Reader from the Centre for Public Health at Queen’s University

The research was conducted by researchers from Queen’s University Belfast, the University of Edinburgh, University of Cambridge, University of Exeter, University of East Anglia and NHS Health Scotland.


  • Claire L. Cleland, Katy McComb, Frank Kee, Ruth Jepson, Michael P. Kelly, Karen Milton, Glenna Nightingale, Paul Kelly, Graham Baker, Neil Craig, Andrew James Williams, Ruth F. Hunter (2019) “Effects of 20 mph interventions on a range of public health outcomes: A meta-narrative evidence synthesis,” Journal of Transport & Health, doi: 10.1016/j.jth.2019.100633



The vast majority of the roads where I live in Bristol England are 20mph.

In my view in any case they represent the maximum speed which you can safely drive at on those streets congested with all sorts of obstacles and elements which obscure vision, mainly parked cars on either side of the street.,

I only push those limits when I am trying to swiftely get past an obsruction on my side of the street, to allow oncoming traffic speedier accesss.

In fact, my view would be that 15mph is what is needed to further improve safety, and the objective should not be to get the maximum number of cars to get to their destinations as fast as they like, but to avoid endangering pedestrians and bicyclists,

It is lovely to live in a neighborhood which is walkable with low rise dense housing and many small shops.

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