Support and compliance study of 20mph speed limits

Drivers’ attitudes to 20mph speed limits don’t necessarily reflect their actual behaviour, with some supporters speeding, while some opponents comply, a study finds. Dr Adrian Davis, Director of the Supporting Healthy Inclusive Neighbourhood Environments Health Integration Team (SHINE HIT), worked with others on the study that explores people’s support of and compliance with 20mph speed limits.

Bristol City Council is one of a growing number of largely urban highway authorities to implement 20mph speed limits on mainly residential streets. Beyond casualty reduction these limits aim to increase social cohesion and physical activity, if streets become perceivably safer places, less dominated by cars.

However, despite high reported support for 20mph speed limits of up to 70 per cent, there are a number of challenges relating to both the support of and compliance with 20 mph speed limits. The study, led by Professors Alan Tapp and Clive Nancarrow, along with SHINE Director Professor Adrian Davis, used a population wide survey of British drivers to explore how support and compliance were interlinked.

Many supporters said they would comply with the limits, and many opponents said they might not comply. But, more surprisingly, some supporters claimed not to comply, while some opponents of 20mph limits were compliers. The findings support a model of driver speeding that offers considerably more complexity than simple mechanisms of attitudes predicting behaviour. Factors included self-enhancement bias, social contagion, and inattentive or automatic driving. There seemed to be a de-coupling of attitudes and behaviour, so that high numbers of drivers apparently contradict their support or opposition for 20 mph limits with their actual driving.

View the abstract online.