Cognitive Load Affects Drivers’ Brake Reaction Time to Longitudinal Conflict through Gaze Concentration and Time Headway Compensation

Driver distraction is one of the main causes of traffic accidents. Previous studies showed mixed conclusions regarding the effects of cognitive load on drivers’ brake reaction time (BRT). To understand how cognitive load affects BRT to longitudinal conflicts, a simulator study was conducted with the performance of a cognitive task during a sudden deceleration of the lead vehicle. First, the result confirmed that drivers increased time headway (THW) as a compensatory behavior and concentrated their gaze toward the road center in cognitive load. Second, based on models comparison, we found that cognitive load affected drivers’ BRT to longitudinal conflicts through two mediators: (1) THW compensation, which leads to a decreased situational urgency and, in turn, increases BRT; and (2) gaze concentration, which leads to an enhanced perception of lead vehicle movement and thus reduces BRT. The findings help understand driver emergency behavior in cognitive load.