Effects of Adaptive Cruise Control and Alert Modality on Driver Performance
Adaptive cruise control (ACC) is a rapidly emerging in-vehicle technology that can enhance or degrade driving safety. A critical factor governing the safety benefit of ACC concerns the driver's ability to assume control of the vehicle in situations that exceed ACC capabilities. The effectiveness of various warning modalities for reengaging distracted drivers during severe braking situations that exceed ACC capability was examined. Warnings that paired a visual icon with sound, seat vibration, or brake pulsation or that combined all three cues were compared. A total of 60 participants drove for 35 min in the National Advanced Driving Simulator. Drivers experienced two severe, four moderate, and eight mild braking situations. ACC could accommodate all but the two severe situations without driver intervention. It also provided a substantial benefit during mild events of lead vehicle braking, enabling drivers to maintain a longer, more consistent minimum time to collision. Unlike performance in previous studies, ACC did not decrease safety during severe braking situations. The combination of a visual icon with sound, seat vibration, or brake pulsation led to slower brake reaction time in severe braking situations, but the grouping of all four warning strategies led to a similar minimum time to collision and maximum braking. In contrast to several previous studies, these results suggest that drivers can effectively assume control when warned that ACC braking authority has been exceeded. Additional research is needed to identify the boundary conditions that specify when drivers can successfully intervene and retake control and whether a multimodal combination of cues can be crafted to speed rather than slow driver response.