Controlled interrupted time series analysis: 20 mph traffic zones
Are low speed zones associated with fewer road injuries?
Road injuries are among the leading causes of loss of life and disability worldwide, and they are projected to make an increasingly important contribution to public health burdens in the coming decades. The researchers aimed to quantify the effect of the introduction of 20 miles an hour (32 km an hour) traffic speed zones on road collisions, injuries, and deaths in London. There is already some evidence that reducing the speed and volume of traffic might reduce rates of road traffic injury. The authors hoped to find clear and convincing evidence that reducing speed is associated with fewer traffic crashes and to quantify the effect of the introduction of a 20 mph speed limit to collisions, injuries, and deaths in London.
The authors performed a retrospective observational study over a 10 year period based on analysis of geographically coded police data on road casualties. They recorded longitudinal changes in counts