Traffic speed zones of 20 mph reduce road injuries and deaths according to research by Grundy and colleagues published in the British Medical Journal.
Road traffic accidents (RTA) are a significant, but often neglected, cause of injury and death worldwide. The WHO estimates that 1.2 million people are killed worldwide in road crashes and up to 50 million people are injured every year. Worryingly, it is predicted that these numbers will increase by 65% over the next 20 years, with a particular burden on public health in low- and middle-income countries.
The researchers analysed road casualties (including fatal and serious injuries) in 119,029 segments of road in London with at least one RTA casualty over a 20 year period (from 1986-2006). The study determined whether the introduction of 20 mph speed zones had an effect on road casualties in these areas (mainly minor roads but including some A and B) and in adjacent roads. There was a steady decline in all road casualties over the 20 yr study period and the length of roads in 20 mph zones has increased. Restricting traffic speeds to 20 mph was associated with a 41.9% reduction in road casualties, with the greatest reductions seen in road casualties involving children. Furthermore, the severity of RTA injuries was reduced with decreased numbers of killed or seriously injured road casualties (including injuries to pedestrians and cyclists). Finally, limiting traffic speeds to 20 mph also slightly decreased road casualties (by 8%) in roads adjacent to the 20 mph zone and there was no displacement of casualties to nearby roads after the implementation of speed restrictions in certain areas.
This study suggests that speed restrictions are an effective means to reduce road casualties in major metropolitan areas like London. However, these restrictions are not appropriate for major roads (A and B roads) and more work is needed to assess alternative strategies to reduce road casualties.
Grundy, C., Steinbach, R., Edwards, P., Green, J., Armstrong, B., & Wilkinson, P. (2009). Effect of 20 mph traffic speed zones on road injuries in London, 1986-2006: controlled interrupted time series analysis BMJ, 339 (dec10 3) DOI: 10.1136/bmj.b4469