Takeover requests for automated driving: The effects of signal direction, lead time, and modality on takeover performance

Vehicle-to-driver takeover will still be needed in semi-autonomous vehicles. Due to the complexity of the takeover process, it is important to develop interfaces to support good takeover performance. Multimodal displays have been proposed as a candidate for the design of takeover requests (TORs), but many questions remain unanswered regarding the effectiveness of this approach. This study investigated the effects of takeover signal direction (ipsilateral vs. contralateral), lead time (4 vs. 7 s), and modality (uni-, bi-, and trimodal combinations of visual, auditory, and tactile signals) on automated vehicle takeover performance. Twenty-four participants rode in a simulated SAE Level 3 vehicle and performed a series of takeover tasks when presented with a TOR. Overall, single and multimodal signals with a tactile component were correlated with the faster takeover and information processing times, and were perceived as most useful. Ipsilateral signals showed a marginally significant benefit to takeover times compared to contralateral signals. Finally, a shorter lead time was associated with faster takeover times, but also poorer takeover quality. Findings from this study can inform the design of in-vehicle information and warning systems for next-generation transportation.