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Evaluating the effectiveness of 20mph 'zones' in reducing road casualties


A review of published evidence has found 20mph ‘zones’ to be effective in reducing the number and severity of traffic collisions and casualties.

The research, funded by the NIHR and conducted by Queen’s University Belfast, 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.

The findings have been published in the Journal of Transport and Health.

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.

Dr Ruth Hunter, Reader from the Centre for Public Health at Queen’s University Belfast explains: “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 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.” 

Dr Hunter added: “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 effectiveness of signage-based speed limits, the impact on public health, and air and noise pollution. We need 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.”

The research was conducted in partnership with researchers from the University of Edinburgh, University of Cambridge, University of Exeter, University of East Anglia and NHS Health Scotland.

The study was funded by the NIHR’s Public Health Research (PHR) Programme.

More information on the study is available on the NIHR Funding Awards website.