There would be widespread congestion when vehicle accidents occur in city river-crossing tunnels, which are usually crucial parts in city road network. Great gradient change at the lowest point of the tunnel makes it more difficult to control the vehicles if the drivers have to make a turn at the same time. This paper researched on the safety of the lowest point of city river-crossing tunnels by building the simulated tunnel scenes through UC-win/Road software and exploring the heart rate of drivers in different conditions through the driving simulator experiments. Controlling variables method was adopted to establish the simplified models and the considered variables were longitudinal grade and radius of horizontal curve. Based on the heart rate data around the time vehicles passing through the lowest point, we defined two new physiological indexes in this paper——the variability of maximum heart rate and the variability of average heart rate to measure the drivers’ physiological load. The driving simulator experiment discovered that the two physiological indexes both had positive correlation with the longitudinal grade while they had negative correlation with the radius of horizontal curve. We also found that there was no big difference of the drivers’ heart rate between the situations with design speed of 60km/h and 40km/h. At last, we evaluated the South Xizang Road Tunnel and the conclusion was that its lowest point was safe for driving.
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