Driving safety evaluation of longitudinal slope and curve combination of extra-long underwater tunnels

Extra-long underwater tunnels are important channels for realising cross-water traffic and play a crucial role in urban traffic. To study the influence of longitudinal slope, curve and combination of both on the driving safety of extra-long underwater tunnels, the physiological changes of drivers under the effect of different combinations of longitudinal slope and curve are analyzed. A driving risk evaluation model is established by introducing the coupling coordination degree, quantifying the relationship between the longitudinal slope, curve radius, and driving risk, and a reasonable combination of the longitudinal slope and curve is selected. The results indicate that there are significant differences in the physiological load of drivers between each longitudinal slope and curve. More specifically, the smaller the longitudinal slope and the larger the curve radius, the smaller the coupling coordination degree and better the driving safety. For a small longitudinal slope area (- 1.5% < longitudinal slope < 1.5%), the minimum curve radius is 400 m, and the ideal curve radius is >= 1700 m. For a small radius curve area (curve radius < 1000 m), the maximum longitudinal slope is - 1.5% (downhill area) and 2% (uphill area), respectively.