Haptic Vibration as Mutual Assistance: Enhancing Driver-Automation Collaboration for Safer Takeovers in Conditional Automation

With increasing vehicle automation, mitigating the performance degradation associated with non-driving-related tasks (NDRTs) is critical for safe transitions to manual control. This study investigated the impact of cognitive load from NDRTs on takeover and post-takeover driving performance in a challenging takeover scenario over a 5-min period. Twenty participants completed simulated drives involving low (resting) or high (two-back) cognitive load NDRTs, with and without amplitude-modulated haptic vibration applied to the lumbar region. NDRTs significantly delayed hands-on response time and impaired lateral control after takeover. Haptic stimulation attenuated these impairments, reducing lane departures and enhancing stability, demonstrating its role as a mutual-assistance mechanism in human-automation collaboration. Heart rate variability analysis showed that the NDRT-related workload persisted after takeover and was partially mitigated by vibration. NASA-TLX confirmed increased subjective workload from NDRTs, with vibration reducing perceived effort. The results support haptic stimulation as a collaborative aid in SAE Level 3 automation.