Relationship between hazard-perception-test scores and proportion of hard-braking events during on-road driving - An investigation using a range of thresholds for hard-braking.

Drivers with higher proportion of hard braking events have greater potential to be involved in an accident. In this study, we tested if hard braking events might be accounted for by drivers' hazard perception (HP) ability. Our investigation was based on an original approach. Usually, researchers define hard braking according to a single deceleration threshold (e.g., g<-0.5). In this study, we chose different thresholds for hard braking (-0.25 to -0.6 g) and for each threshold, we examined the linkage between HP test (HPT) scores and the proportion of hard braking events. We hypothesized that this linkage would be stronger if the threshold that defines hard braking is higher. This is because the stronger the braking events, the higher the likelihood that they resulted from later detection of hazards and the lower the likelihood that they resulted from other causes (e.g., road humps). Thirty-three drivers completed an HPT and used a smartphone app that recorded their vehicle kinematics. We estimated the coefficient of HPT score in a series of binomial regression models on the proportion of hard braking events. In accordance with our hypothesis, we found that the coefficient of HPT score changed as a function of the threshold for hard braking. This finding was based on a significant negative Spearman correlation between the coefficients and the threshold and on linear functions that we derived from two binomial models that allowed the coefficient of HPT to vary according to the threshold. Our findings show that hard braking events are related to HP ability and can inform safety interventions in response to excessive proportion of hard braking events. In addition, they demonstrate that using a range of thresholds for hard braking is a practical tool in the study of hard braking events. From a theoretical perspective, our findings provide strong support to hazard perception theory.