Simulation Analysis of the Distance Between Tunnels at the Bridge-Tunnel Junction of Mountainous Expressway on Driving Safety Under Crosswinds

To analyze the influence of the distance between tunnels at the bridge-tunnel junction in the mountainous area on the driving safety under crosswind, a vehicle dynamics model is established by Carsim software. Under the conditions of different driving speeds (60km/h, 80km/h and 100km/h), different wind scales (level 6–9) and three alignment combinations of the tunnels (tunnel-straight road-tunnel, tunnel-curving road-tunnel, tunnel-the combination of straight and curves road-tunnel), the vehicle’s lateral offset and lateral force coefficient are used as evaluation indexes to study the influence of distance between tunnels on driving safety. When the distance is small, the lateral offset and lateral force coefficient of vehicle driving on the bridge-tunnel junction increase firstly and then decrease as the distance increases. But the changes of the lateral offset and lateral force coefficient are not synchronized, and the peak value of the lateral force coefficient occurs earlier than the lateral offset. Finally, the minimum safety spacing of each condition and speed limits for different distances are proposed. Under the condition of the straight-tunnel, 20m distance between tunnels cannot ensure the driving safety when the wind scale reaches level 9, and the road should be closed. Under the conditions of the curve and the combination of straights and curves, driving safety cannot be maintained at each spacing at wind scale level 8 and 9, and the road should be closed. However, when the wind speed is level 6 or 7, speed limits can be adopted to ensure driving safety. The results suggest that vehicles’ lateral offset and lateral force coefficient can be effectively reduced by reducing the driving speed or increasing the distance between tunnels, so the risk of accidents caused by the crosswind can be reduced.