Driving simulation to support road safety policy: Understanding crash risks to better inform speed setting guidelines

Currently, selection of the appropriate speed limit for a given road segment is based on road authorities’ consideration of a number of environmental criteria. These include: cross section, alignment, and the number and type of abutting developments and traffic; the movement of and potential for conflict with other road users; the road’s crash history; and seasonal influences such as holiday traffic. Observed crash data demonstrate a clear lack of uniformity in crash risk across sites within the same speed limit zone, suggesting that, if speed limits were set for safety reasons alone, there are other factor(s) affecting crash risk which are not, currently, being considered.

Driving simulators are often used to evaluate a wide variety of road safety interventions for their effects on driving performance and speeding behaviour. Policy makers and regulators tend to question, however, whether results from simulator-based research can and should be used to reliably predict actual changes in real-world crash risk. This paper reviews issues related to simulator validity and fidelity, and presents three psychological constructs, driver workload, situation awareness, and hazard perception, that can be measured in the driving simulator and are commonly used as ‘surrogate’ measures of crash risk. Driving simulation offers a safe, low cost method to identify and investigate environmental factors affecting crash risk which are not, currently, included in speed setting guidelines. By providing for a more complete account of the factors that affect crash risk, the inclusion of these features in future speed setting or road design guidelines could be expected to lead to reductions in crash risk and, consequently, enhanced overall road safety.