The impact of spiral tunnel characteristics on driver HRV and stress perception: A naturalistic driving experiment

This study examined the impact of the combined configuration of spiral tunnel length and radius on drivers' heart rate variability (HRV) and stress perception through a naturalistic driving experiment with 30 participants. Three spiral tunnels varying in both length and radius were evaluated, and the effects of uphill and downhill driving directions were also considered. The results revealed that the combined configuration of tunnel length and radius significantly influenced drivers' physiological and psychological states. Specifically, longer tunnels with smaller radii were associated with increased average heart rate (HR), decreased standard deviation of normal-to-normal intervals (SDNN), elevated low frequency to high frequency ratio (LF/HF), and reduced sample entropy (SampEn), all indicating heightened stress responses. Uphill driving consistently led to higher average HR, lower SDNN, and higher LF/HF ratio compared to downhill driving, reflecting increased stress due to greater physical and mental demands. These findings offer invaluable insights for the design and management of spiral tunnels, with the ultimate goal of enhancing driver safety and comfort. By optimizing tunnel characteristics and implementing appropriate traffic management strategies, it is possible to create a more favorable driving environment that mitigates the negative impacts on drivers and promotes overall well-being.