Is a focus on low level speeding justified? Objective determination of the relative contributions of low and high level speeding to the road toll

Speed is the largest single behavioural contributor to the road toll both in Australia and globally. While the community accepts that high level speeding (say 30+ km/h over the speed limit) is dangerous, there is more acceptance of low level speeding (say within 10 km/h of the speed limit) and considerable debate about the risk it poses. Broadly, the debate has not had an objective base.

Objective evidence can be reconstructed. Explicitly, data on the increasing risk of a serious crash for each increment of speeding can be combined with objective on road surveys of actual speeding behaviour. The direct multiplication of the increased risk for each 5 km/h above the speed limit by the number of drivers speeding by that amount reveals the total risk in each category.

We conducted this analysis using speed surveys from every speed limit in NSW, and several studies of relative risk of speeding. Kloeden et al.’s studies of speeding and crash risk in urban and rural environments and the Nilsson Power Model were used as the basis for determining the contribution of low and high level speeding to road related fatalities and injuries. These analyses reveal that despite the much lower risk per driver, the large number of drivers speeding at low levels makes this category of speeding a major road safety problem.

Results are discussed with regards to public attitudes to speeding and implications for policies aimed at reducing the involvement of speeding in the road toll.