Stopping behaviour of drivers distracted by mobile phone conversations

Increased cognitive load—due to talking on a mobile phone whilst driving—has been shown to impair decisions and actions of distracted drivers in numerous ways including speed selection, lane keeping, and compliance with traffic signals to name a few. In contrast, the stopping behaviour of distracted drivers has not been examined in detail, despite the fact that improper stopping might lead to rear-end and angle collisions. As such, the aim of this study was to examine the stopping behaviour of drivers distracted by a mobile phone conversation. In particular, the stopping behaviour of drivers after detecting a pedestrian entering a zebra crossing was examined. The CARRS-Q Advanced Driving Simulator was used to test participants on various simulated driving tasks including an interaction with a pedestrian at a zebra crossing. Thirtytwo licensed drives drove the simulator in three phone conditions: baseline (no phone conversation), hands-free and handheld. In addition to driving the simulator, each participant completed questionnaires related to driver demographics, driving history, usage of mobile phones while driving, and general mobile phone usage history. The drivers were 21 to 26 years old and split evenly by gender. An analysis of speed profiles along the roadway before the pedestrian crossing revealed increased decelerations among distracted drivers, particularly during the initial 20 kph speed reduction. Drivers’ initial 20 kph speed reduction time was modelled using a parametric accelerated failure time (AFT) survival model with a Weibull distribution and clustered heterogeneity, accounting for the repeated measures design. Factors significantly influencing the survival time included vehicle dynamics variables like initial speed and maximum deceleration, driver-specific variables such as phone condition, crash involvement history, and self-reported experience using a mobile phone whilst driving. Distracted drivers on average appear to reduce the speed of their vehicle faster and more abruptly than non-distracted drivers, revealing an element of risk compensation. Abrupt stopping by distracted drivers might pose significant safety concerns to following vehicles in a traffic stream.