Assessing speeding propensity via self-report: An on-road validation study of the Driver Behaviour Questionnaire and three speeding-specific measures

Abstract

Speeding is well-established as a key contributor to crash risk and severity, yet it remains a common behaviour. Hence, speeding propensity is an important focus of study in road safety research. For pragmatic reasons, researchers investigating the causes and consequences of speeding behaviour, or evaluating interventions, will often need to measure speeding propensity indirectly, via self-report (e.g., in large-scale online studies). In the present study, we evaluated a number of self-report measures of driving behaviour. Specifically, we investigated several Driver Behaviour Questionnaire (DBQ) scales (All Violations, Ordinary Violations, Aggressive Violations, and Errors), as well as three speeding-specific measures, namely: (1) the DBQ Speed Items; (2) the Speed Scale from the Driving Style Questionnaire (DSQ); and (3) a novel measure of Relative Speed Choice. In the present study, we assessed the extent to which scores on these measures reflect actual risky speeding behaviour during real driving (as a construct closely related to speeding propensity). To achieve this, we used data from g-force triggered dashcams to estimate the frequency of young drivers’ speed-related heavy-braking events (i.e., incidents in which the participant was exceeding the speed limit and then applied the brakes abruptly) over an average of 6.43 weeks. Among the standard DBQ scales, only Ordinary Violations scores were significantly associated with the frequency of speed-related heavy-braking events. However, compared with DBQ Ordinary Violations, scores on all three speeding-specific measures were better predictors of these events. Further, both the DSQ Speed Scale and the Relative Speed Choice measure provided better prediction than the DBQ Speed Items. We also found that prediction could be further improved (to a small degree) by using both the DSQ Speed Scale and the Relative Speed Choice measure in combination. These results suggest that the DBQ Ordinary Violations scale, the DBQ Speed Items, the DSQ Speed Scale, and the novel Relative Speed Choice measure can all potentially be used to assess speeding propensity in studies where drivers’ risky speeding behaviour is of interest, but the latter two (alone or in combination) are the best options from a measurement perspective.