The Length Definition of the Expressway Tunnel Based on Driving Safety and Comfort

The road tunnel which has advantages of improving the alignment criterion, educing travel distance, protecting the natural environment is increased used in China. At present, the related domestic and foreign researches are mainly based on the design scale, lining type, construction methods and difficulty, use and so on. There is little about the length definition of road tunnel based on the drivers' driving safety and comfort. The driver is client of tunnel. The driving environment of tunnel is different from the outside and tunnel length has impact on the driving safety and comfort. So this paper defines the length of the tunnel based on driving safety and comfort in order that the related scholars who concern and study the tunnel treat them differently. By analyzing the safety and comfort test data of 62 tunnels, we get the shortest tunnel whose length is 450m based on the evaluation index of driving safety and comfort-workload. When the length is less than 450m, the drivers' workload is low and stable, such tunnels have no significant impact on the driving safety and comfort; When the length is greater than (or equal to) 450m, the drivers' workload becomes a apparent and consistent law that it increases at the entrance of the tunnel, shows no significant change in the tunnel, it increases again until the tunnel exit. The increased workload is with a certain lead or lag. Because this has a large influence on the driving safety and comfort, we need to consider some safe measures.