A Simulator Study on the Minimum Safety Net Distance between Tunnel and Interchange Exit of Mountainous Expressway

In the design of some mountainous expressways, the spacing between tunnels and interchanges usually can’t meet the requirements of the design specification because of the limitation of mountainous terrain and the scope of land use. In order to research the minimum safe distance between tunnel and interchange exit under the condition of insufficient length of subgrade, an experimental study was carried out by driving simulator. The virtual simulation scenario of the six-lane mountainous highway with a design speed of 80 km/h was established according to a real road engineering project, and four kind of net distance between the tunnel and the interchange exit were taken as the experimental conditions. Speed and lane crossing points were selected as key evaluation indicators to study the driving risk of drivers on such road section. The results o show that:(1)the net distance between tunnel and interchange exit has a significant impact on the lane crossing position when the driver leaves the main line;(2)under the condition of limited length of subgrade, there is not a good safe driving environment for drivers to drive out of the main line from the inner lane. Finally, based on the driving behavior analysis results, the design recommendation value of the minimum safety net distance between tunnel and interchange exit is proposed, and the corresponding suggestions for traffic organization are also put forward.