The effects of ACC headway time configuration on drivers' overtaking tendency in a driving simulator

The preference to maintain a certain desired speed is perhaps the most prevalent explanation for why a driver of a manually driven car decides to overtake a lead vehicle but motivation for overtaking is also affected by other factors such as aggressiveness, competitiveness or stress caused by following another vehicle [1]. Whether such motivational factors for overtaking play a role in partially automated driving is yet to be determined. This study had two goals: (1) to investigate whether and how a driver's tendency to overtake a lead vehicle changes when driving a vehicle equipped with an adaptive cruise control (ACC) automated system. (2) To study how such tendencies change, when the headway time of the automated system varies. Following [2] it was also decided to manipulate the speed of the lead vehicle. Participants drove three 8-10 minutes simulated drives under light traffic conditions in a driving simulator under both manual and level 1 automation driving conditions. The automation condition included an ACC with two headway time configurations: 1 sec and 3 sec. Each drive included six passing opportunities representing three different speeds of the lead vehicle (-3 km/h, +3 km/h, +6 km/h relative to the participant) once with variance and once without. Results show that drivers tended to overtake a lead vehicle more often in manual mode than in both modes of automated driving. ACC with headway time of 1 sec led to more overtaking events than ACC with 3 sec headway time. In addition, the relative speed of the lead vehicle and its variance also had an effect on overtaking tendencies. This work has shown that driving with ACC might be helpful in reducing overtaking frequencies and to a larger extent when the headway time is set to 3 sec. The implications of this study are discussed.