From Manual to Automated Driving: Understanding the Shift in Driver Headway Preferences

A common feature in Automated Vehicles (AVs) at different levels of automation is Adaptive Cruise Control (ACC), which helps drivers to choose their desired headway to a preceding vehicle from pre-defined options, improving comfort and traffic efficiency. However, the acceptance and use of ACC depend on how well these options align with users' expectations with different driving styles. Therefore, using a driving simulator and recruiting 28 participants, this study aimed to examine how the driver's headway preferences differ from their manual driving behaviour considering their personal driving styles and to identify the factors that shape this deviation. Additionally, the discrepancy between the available headway settings and the preferences of drivers and its impact on trust and perceived safety of users were explored. The participants experienced three scenarios, in the first they drove manually, in the second they defined their preferred time headway, and in the third they selected a desired headway setting from three available options. The results showed that drivers, in general, prefer a larger headway for ACC compared to their manual driving, although this preference depends on their personal driving styles. Along with the "dissociative" self-reported driving style, average manual time headway and conscientiousness personality trait affect the difference between drivers' manual and preferred time headway. The study found that while exposure to ACC increases trust in AVs, perceived safety decreases if headway settings do not match drivers' preferences, discouraging AVs use.