Unraveling the complex interplay between curved tunnels and drivers’ physiological responses: An HRV perspective

This study aims to unravel the complex interplay between curved tunnels and drivers’ physiological responses from an HRV (Heart Rate Variability) perspective. A group of 30 individuals with valid driver’s licenses was selected, and their HRV was monitored while driving through four curved tunnels in Yunnan Province, China. HRV indicators such as RMSSD (Root Mean Square of Successive Differences), SDNN (Standard Deviation of Normal-to-Normal Intervals), LF (Low Frequency), and LF/HF (ratio of Low Frequency to High Frequency) were analyzed. The independent variables included tunnel radius, turn direction, and zone characteristics. The results demonstrated that the radius, turning, and zone of the curved tunnel significantly influenced drivers’ HRV. Specifically, as the tunnel radius decreased, the mean RMSSD and SDNN of drivers decreased, while the mean LF and LF/HF increased. In left turns, drivers had lower RMSSD and SDNN values but higher LF and LF/HF ratios compared to right turns. Additionally, drivers showed the highest mean RMSSD and SDNN in the entrance zone of the tunnel, followed by the middle zone, and the lowest in the exit zone. Conversely, the exit zone had the highest mean LF and LF/HF, followed by the middle zone, and the entrance zone had the lowest. These results indicate that the characteristics of the curved tunnel have a substantial impact on drivers’ physiological responses. A smaller tunnel radius leads to increased stress and cognitive load, as reflected by the decreased HRV metrics and increased sympathetic activity. Turning maneuvers, particularly left turns, result in asymmetry in autonomic responses, with lower RMSSD and SDNN and higher LF and LF/HF during left turns. The variations in HRV across different zones within the tunnel suggest that environmental cues play a role in sympathetic activation, with the exit zone showing the highest sympathetic activity. These findings offer significant insights into the relationship between tunnel conditions and drivers’ physiological responses, emphasizing the importance of considering these factors in road safety and human factors engineering. By comprehending how tunnel characteristics affect drivers’ autonomic nervous system responses, we can formulate strategies to enhance driver well-being and safety.