What is the optimal display range? Exploring the impacts of area and shape on in-vehicle head-up display efficiency.

In-vehicle Head-Up Displays (HUDs) are expected to incorporate more information in the future, necessitating deeper understandings of design properties that can enhance display safety and efficiency. However, the optimal display characteristics-particularly in terms of area and shape-remain inadequately understood. This study investigated these two factors by manipulating horizontal and vertical Field of View (FOV) angles within a simulated in-vehicle HUD. Thirty-one participants participated in this laboratory-based study they completed a digit matching task while driving within a driving simulator. The accuracy and response time of the task served as indicators for efficiency. The standard deviation of lateral position (SDLP) was employed to assess area and shape's impacts on driving performance, alongside subjective ease-of-use evaluations. Results indicated that an increase in horizontal FOV angle significantly delay response times and reduce ease-of-use ratings. We also observed significant effects of area and shape on response time and ratings; specifically, participants responded faster in smaller display area conditions, which were also rated as the easiest to use. Accuracy, however, was largely unaffected by size and shape. Importantly, most manipulations did not interfere with driving performance, except for the area 500 condition, wherein landscape shape was associated with better lane-keeping performance. Our findings provide valuable insights for the design of in-vehicle HUDs.