Spatial variation characteristics of drivers' visual search behavior at urban expressway exits

This study aims to reveal the spatial variation characteristics of drivers' visual search behavior in urban expressway exit areas by analyzing the evolution patterns of their fixation characteristics and fixation transition patterns along the driving path. The ultimate goal is to establish a human factors foundation for enhancing safety and optimizing the design of traffic facilities in these areas.

Two types of exit ramps-short and long-were selected as experimental scenarios. A naturalistic driving experiment was conducted, collecting eye-movement data from 25 participants. Their eye-movement data were analyzed by dividing the visual field into three primary Areas of Interest (AOIs): Guiding, In-car, and Look-ahead fixations, and by segmenting the exit routes spatially. Key metrics, including the proportion of fixation duration, fixation entropy, fixation transition probability, and fixation transition entropy, were calculated for each segment to quantify visual search behavior.

As vehicles approached the exit, visual attention progressively concentrated on Look-ahead fixations, peaking at 91% within 50-100 meters before the exit. Drivers exhibited high fixation entropy and broader search dispersion in two critical sections: from ramp entry to 50 m past the gore point, and 50 m before the ramp terminal. However, attention to Look-ahead fixations increased again toward the end of the ramp, indicating a stabilization of visual scanning patterns. For short ramps, drivers primarily focused on Guiding fixations, with fixation duration exceeding 50% across all segments from the gore point to the ramp terminal, and the transition probabilities from both Look-ahead fixations and In-car fixations to Guiding fixations exceeding 56%. In contrast, drivers navigating long ramps exhibited higher fixation entropy and fixation transition entropy, reaching local peaks before entering curved sections.

This study reveals that drivers dynamically adjust their visual search strategies based on their spatial position at urban expressway exits. As the vehicle approaches the exit, visual attention prioritizes information acquisition for decision-making, before shifting back to vehicle control near the exit point. In short ramps, drivers exhibited a heightened demand for lane control, whereas the complex geometry of long ramps increased task complexity, necessitating simultaneous information search and vehicle control and leading to more sophisticated visual strategies. These findings elucidate the intrinsic link between drivers' visual search behavior and their spatial positioning, providing a human factors foundation for optimizing the spatial compatibility of traffic facilities.