Factors affecting the severity of rear-end conflicts: A driving simulator study

Traffic conflict has been adopted as a road safety surrogate measure, especially for specific road entities and road user groups. It is believed that factors affecting the occurrence and severity of traffic conflicts would also affect those of road crashes. In this study, the effects of driver age, traffic condition and driving time on the severity of rear-end conflicts on inner-city roads were examined using driving simulator approach. A total of 41 drivers completed the driving simulator experiment. Their responses to 82 challenging events were assessed. Performance indicators including braking reaction time (BRT), minimum time-to-collision (TTC _min), time exposed time-to-collision (TET), time integrated time-to-collision (TIT) and the conflicting speed were considered. A TTC _min of 3 seconds or less was adopted as a threshold to screen out 68 rear-end conflicts for subsequent analysis. Results indicated that low traffic flow condition contributed to the reductions in BRT, TIT and TET. Drivers tend to react faster to the challenging event under the low traffic condition. Also, the rear-end conflicts tend to be less severe under the low traffic condition. Elderly drivers were found to have a shorter duration of safety-critical situation during the rear-end conflicts. Driving time has significant influence on BRT, TIT and TET. Driver's reaction was slower at the last five minutes of the simulated driving. This could be explained by the driver fatigue due to the prolonged driving. However, the adaptive strategy, i.e. speed reduction, in the late period of the 60-minute driving contributed to the lower severity level of conflict. This study should provide useful insights on the traffic conflict analysis, using driving simulator approach.