Analysis of driver's physiological responses and task load in curved and spiral tunnels: A naturalistic driving experiment

This study aims to analyze the physiological responses and task load of drivers in curved and spiral tunnels. Spiral tunnels, a unique solution for complex terrains, exhibit distinct geometric and functional characteristics compared to curved tunnels. Despite advances in spiral tunnel design in China, concerns about driver safety persist. The research recruited 30 participants to conduct naturalistic driving experiments in curved and spiral tunnels. By analyzing heart rate variability (HRV) indices and using factor analysis, four HRV indices (HR, SDNN, LF/HF, SampEn) were selected as primary indicators. Results from statistical analysis showed that drivers had a significantly higher average heart rate (HR) in spiral tunnels compared to curved tunnels (F(1,1198) = 593.29, p < 0.01), indicating greater psychological stress and physiological burden. The standard deviation of NN intervals (SDNN) was lower in spiral tunnels (F(1,1198) = 868.18, p < 0.01), suggesting reduced heart rate variability and a more dominant sympathetic tone. The ratio of low-frequency power to high-frequency power (LF/HF) was higher in spiral tunnels (F(1,1198) = 419.85, p < 0.01), indicating increased sympathetic nervous system activity. Additionally, the sample entropy (SampEn) of the electrocardiogram was lower in spiral tunnels (F(1,1198) = 1595.05, p < 0.01), suggesting a decrease in the complexity of the ECG signal and a weaker autonomic nerve regulation ability of the heart. Subjective task load evaluation using the NASA-TLX scale further revealed that drivers experienced a higher task load across various dimensions such as mental demand, physical demand, temporal demand, effort, frustration, and performance in spiral tunnels. In summary, this study provides valuable insights into the physiological and psychological responses of drivers in curved and spiral tunnels, contributing to optimizing tunnel design, improving driver education and training, and enhancing tunnel safety and the overall driving experience.