Combined effect of traffic and geometrics on rear-end collision risk: driving simulator study

This paper presents the results of a laboratory experiment that sought to analyze rear-end collision risk under various traffic conditions and given various road geometric configurations. The CRISS (Inter-University Research Center for Road Safety) interactive fixed-base driving simulator was used. An 8-km, two-lane, rural road that incorporated 15 tangents and curves was designed and implemented in the driving simulator. Four distinct traffic conditions were simulated, and 32 drivers drove in four traffic scenarios. The differences in speed and position between each driver’s vehicle and other vehicles on the road were collected to calculate two safety indicators, which the scientific literature has suggested to evaluate rear-end collision risk on the basis of the time-to-collision (TTC) notion. The maximum values of these indicators were given for an average traffic-flow condition, which is therefore the most critical condition for rear-end collision risk. In scenarios that entailed lower traffic volumes, significant models of TTC-based indicators were found for tangents with lengths that ranged from 400 m to 1,000 m. The independent significant variables were volume-to-capacity ratio, length of the tangent, and length of the curve approaching the tangent. In traffic scenarios characterized by higher traffic volumes, no significant models were found for any kind of geometric element. This outcome seems to prove that the influence of the geometric features on the rear-end collision risk tends to become negligible whenever the volume-to-capacity ratio reaches high levels. In these conditions driver behavior is exclusively affected by interactions among vehicles.