Hysteresis effect of comprehensive driving risk in highway tunnel-group: A naturalistic field test study

Driving through tunnel-group sections in mountainous highway involves frequent abrupt changes in the driving environment, which can easily induce fluctuations in driver workload and elevate driving risk. To investigate the variation patterns of driving risk in tunnel-group sections, this study utilized naturalistic field test data and focused on drivers' heart rate variations, pupil characteristics, and driving behaviors. An evaluation index system was established covering aggressive driving behavior, driving workload, and speed-variability-related risk indicators. All indicators were normalized, and a hybrid weighting scheme was adopted by integrating the CRITIC method with the entropy weight method. The comprehensive risk index for each sub-section of the tunnel group was then calculated using a linear weighted approach. The results indicate that driving risk is more sensitive in tunnel entrance and exit sections. As the number of traversed tunnels increases, the overall tunnel driving risk shows a decreasing trend, demonstrating a pronounced hysteresis effect. Moreover, the hysteresis intensity varies significantly with longitudinal spacing length, i.e. the longer the longitudinal spacing, the greater the decrease scale of driving risk for each tunnel within the tunnel group, indicating a stronger hysteresis intensity. Specifically, the decrease scale of the maximum comprehensive driving risk index increased from 0.06 and 0.08 in short-spacing tunnel groups to 0.09and 0.10 in medium-spacing tunnel groups, and further to 0.10and 0.11 in long-spacing tunnel groups. The comprehensive driving risk index developed can effectively characterize the risk evolution and key influencing factors in continuous tunnel groups. The identified risk evolution patterns provide a basis for safety optimization of longitudinal spacing in tunnel groups and can guide the rational deployment of lighting and visual guidance facilities, thereby improving overall driving safety.