Reductions in driver speed using posted feedback of speeding information: Social comparison or implied surveillance?

Abstract

Reducing driver speed has an essential role to play in traffic safety. This study measured the effect of a roadside sign, in a 50 km/h zone, that consecutively displayed one of three messages: 1. The average speed at the site: this message was designed to induce “social comparison” whereby drivers may reduce their speed in order to comply with the behaviour of the majority. 2. A warning that drivers’ speeds were being measured: this was intended to imply surveillance whereby drivers may reduce speed in order to avoid possible enforcement action. 3. A combination of both messages, to see if both together would have a greater effect than either alone. The speed of drivers travelling along a busy urban road (11,500 cars daily in each direction) was measured using inductive loop detectors. The proportion of drivers travelling 60 km/h or less increased with all three messages, suggesting that both social comparison and implied surveillance are mechanisms by which driver speed may be reduced. However, the speed reductions were not as great as in previous studies of feedback signs. This may be due to differences in the existing safety culture.