From brake lights to beyond – exploring information needed for car-following behaviour

The rear-end crash is highly related to the car-following (CF) behaviours. Increasing evidence suggests that, in addition to direct leading vehicle (DLV) information, considering beyond-visual-range (BVR) and implicit information when following the traffic flow can reduce collision risk. However, to date, little is known about drivers’ needs for BVR and implicit information in CF events. Thus, to guide the innovation of external human-machine interface (eHMI) design, which aims to facilitate safer CF behaviours, we adopted a two-stage approach, including a focus group study (N=38) and a field study (N=30) to understand drivers’ information needs and the decision-making process in CF events. Participants included drivers from various professions and with diverse driving experiences. Through thematic analysis, we found that drivers’ CF behaviours depend on more than relative motions between the subject vehicle and the DLV, but also on the traffic conditions (congested or not), the behaviour, mental state, and driving style of the leading driver, the traffic flow ahead, and even the behaviour of the following vehicle. At the same time, drivers have high expectations of BVR information on eHMIs when following traffic. This study offers insights into CF behaviour and eHMI design aimed at reducing rear-end collisions.