Effect of longitudinal slope of urban underpass tunnels on drivers' heart rate and speed: A study based on a real vehicle experiment

To study changes in physiological and behavioral characteristics in longitudinal segments of urban underpass tunnels, 22 drivers were selected to perform an experiment. An MP150 multi-conductivity physiological recorder and ECU speed acquisition equipment were employed to record and analyze the drivers' heart rate and speed. The index of heart rate growth (HRG) was proposed to analyze the psychological changes, and a scatter chart was used to analyze changes in HRG. Models of the relationships between HRG, speed, and slope were developed to quantify the impact of slope on HRG and speed. The results show that HRG is significantly higher when driving downhill in a tunnel than when driving uphill, indicating that drivers are more nervous when driving downhill. The fluctuation of HRG when driving downhill in a tunnel is significantly greater than when driving uphill, and the peak value is also larger, indicating that the drivers' psychological fluctuations are greater and the degree of psychological tension is higher when driving downhill in a tunnel; thus, drivers should be cautious when driving downhill. The results also show that slope has a major influence on HRG and the speed of the vehicle, and the safe slope and driving speed when driving uphill and downhill in urban underpass tunnels were obtained. Finally, the proposed values of safe slope and safe speed in urban underpass tunnels are given based on the actual safety and control situation.