Effects of Readiness Deprivation on Takeover With Varying Time Budget in Conditional Automated Driving Scenarios

As vehicle automation levels rise, future automated driving systems can enable drivers to engage in nondriving-related tasks (NDRTs). However, drivers remain responsible for driving safety. In the case of an automated vehicle failure, a driver must disengage from their NDRTs and take control of the vehicle. When fully engaged in NDRTs during Level 3 automation, NDRTs can compete for the resources for driving tasks, thereby depriving cognitive and physical readiness. This study investigated how compromised driver readiness affected takeover performance in situations with varying urgency levels. A simulated driving experiment was conducted with 32 participants in four states of readiness deprivation created through NDRT assignment, and two time budget levels were applied to represent multiple urgency scenarios. First, subjective ratings on readiness deprivation showed that depriving drivers of one form of readiness (i.e., cognitive or physical) adversely affected the other. Furthermore, retaining cognitive readiness may provide greater self-assessed utility. The NDRTs with similar interaction attributes generate comparable readiness deprivation ratings, offering a systematic way to evaluate their impact on takeover. Then, the impact of readiness deprivation on takeover performance varied significantly based on time budgets. With ample time, depriving drivers of physical or full readiness increased takeover time. However, these delayed actions, combined with stable lateral control, suggested a safe takeover strategy aimed at readiness recovery. Conversely, limited time hindered this recovery. Drivers performed takeovers despite impaired readiness, resulting in quicker but often abrupt post-takeover lateral movements. Notably, takeover actions were initiated once both cognitive and physical readiness were achieved, regardless of the time budget.