Road traffic injuries, a leading cause of death and disability worldwide

20 mph traffic speed zones reduce casualties by 41.9% with the greatest reduction in child casualties, according to research published today in the British Medical Journal.

Road traffic injuries are a leading cause of death and disability worldwide and are projected to make an increasingly important contribution to public health burdens over the coming decades, especially in low- and middle-income settings.

While the UK has a comparatively good road injury record, with among the lowest rates in Europe, there were still 2,858 deaths and 26,066 serious injuries in the roads in England and Wales in 2006, and reducing this number remains a major aim of public policy. Over the last 15 years or so, in London, as in many areas of the UK, 20 mph zones have been established.

A team from the London School of Hygiene & Tropical Medicine have estimated the effect of introducing 20 mph traffic speed zones on road collisions, injuries and fatalities in London.  They carried out an observational study based on analysis of geographically-coded police road casualty data, from 1986 to 2006. Overall, the introduction of 20mph zones was associated with a 41.9% reduction in road casualties, after allowing for underlying time-trends.

The percentage reduction was greatest in younger children, and was greater for people killed or seriously injured in collisions. Pedestrian injuries were reduced by a third with a greater reduction in children aged 0-15 years. The reduction was smaller in cycling casualties (17%) but again this was higher in children.

Chris Grundy, Lecturer on Geographical  Information Systems at the London School of Hygiene & Tropical Medicine and lead author of the study, comments: 'This study provides the most detailed evidence to date of the effect of 20 mph zones on road casualties and collisions in major metropolitan areas. 20 mph zones appear to reduce casualty numbers, especially serious injury and death, and suggest that the benefits are greatest among younger children 'In the context of the wider evidence about the health burdens associated with road injuries, this evidence supports introducing 20 mph zones in major British cities and also in similar metropolitan areas elsewhere. Indeed, even within London, there is a case for extending the currently limited provision of such zones to other roads with high numbers of casualties.'