Effects of AR-HUD forward collision warning designs on drivers’ braking behavior and visual attention in highway driving: an eye-tracking study

While augmented reality head-up displays (AR-HUDs) are known to enhance forward collision warning (FCW) safety, the optimal design for highway scenarios remains unclear. This study evaluated three AR-HUD FCW designs, including spatial referencing (SR), scaling animation (SA), and static symbol (SS), against a no-warning baseline in a driving simulator experiment with 39 participants. Results showed that SS produced the fastest brake response, higher time-to-collision, and fewer collisions. SR demonstrated the most stable visual attention pattern, reflected by lower pupil diameter variability, saccade time ratio, and dwell time at the hazard area, and received the highest usability ratings. SA showed a moderate effect without achieving the response efficiency of SS or the visual attention of SR. These findings provide theoretical insights into how FCW visual representations influence driving performance and visual attention, offering design insights to mitigate rear-end collision risk and improve highway safety.