Effect of Police Presence on Urban Driving Speeds

This paper describes a study of the effect of police presence on traffic speeds on urban streets, particularly the memory effect, ie, drivers reduce their speed in areas where they have previously seen enforcement symbols, even when no enforcement symbols are present. A police car was present at two sites for a number of days in February and March 1982, with their presence being gradually reduced over the following days. Speed surveys were carried out before, during and after the enforcement period. The results showed that the presence of a police vehicle reduced the proportion of vehicles exceeding the speed limit by approximately 70 per cent and with commuter traffic this effect lasted at least two days after the enforcement was removed. It was also shown that drivers quickly resumed their normal driving behaviour after passing a police vehicle. The major conclusion of the study was that police traffic law enforcement was most suitable for reducing speeds at chosen problem sites. However, given the current low level of resources, enforcement cannot be expected to generally reduce urban driving speeds. (Author/TRRL)