Drivers' dynamic perception of accident risk and safety in underground road merging areas

The multi-entry underpass road tunnels is affected by various factors, including long downhill approaches outside the tunnel, monotonous visual environments inside the tunnel, underground merging of the main and secondary roads, and limited sight distance and sight zone. These combined conditions can lead to perception and judgment errors among drivers, significantly increasing the accident risk of rear-end and lateral crashes. This study used video data from a real vehicle test and conducted a subjective perception experiment with a driving simulator. It collected key indicators related to crash accident risk and prevention, including Identify Merging Time (IMT), Perceive Hazard Time (PHT), and Assess Safety Time (AST), to analyze the dynamic perception of risk and safety at the entrances of the main and secondary roads under 6 different speeds. And a Linear Mixed Model (LMM) was applied to evaluate the effect of speed on each indicator. Results showed that IMT decreased with increasing speed for both main and secondary roads, with the main road exhibited the highest Identify Merging Delay Rate (IMDR) at 38.667 %, indicating that drivers traveling at higher speeds struggled to identify the underground merging area in time. The Perceive Hazard Distance (PHD) for both main and secondary roads extended with increasing speed. Compared to the main road, drivers on the secondary road perceived hazards earlier within 38.167 to 46.683 m downstream of the physical gore point. This earlier perception was related to their frequent use of rearview mirrors to assess merging opportunities and the expanded sight zone in the secondary road merging area. Through LMM analysis, secondary road drivers' PHD is less dependent on speed and is more influenced by the merging process itself. Overall, at higher speeds, reaction time is notably reduced, leading to delayed identification, hazard perception, and safety assessment. Hence, these findings provide valuable references for optimizing underground merging area design and enhancing drivers' safety perception in multi-entry underpass road tunnels.