Slack effect test at exit of extra-long highway tunnels

To study the influence of the slack effect at the exit of extra-long highway tunnels on traffic safety, a vehicle test was carried out. Data on the luminous environment, vehicle speed, and pupil area and attention distribution of drivers were collected to explore the mechanism of the slack effect. Multiple control scenarios were set up to conduct driving simulation tests. The lag effect of the slack effect in the post-tunnel zone was discussed, and the influence distance and harm of slack effect were further analyzed. Analysis results show that, the illumination at the tunnel exit increases rapidly, the pupil area changes quickly, and the white hole effect occurs. While the luminous environment undergoes drastic changes, abnormal phenomena appear such as reduced driver attention and increased vehicle speed. The slack effect at the exit of an extra-long tunnel is thus verified. The slack effect is coupled with the white hole effect, which leads to abnormal driver attention and vehicle speed, along with visual disorder, posing a serious threat to driving safety. In the departure and the post-tunnel zones after the tunnel exit, drivers are still affected by the slack effect. Compared with ordinary roads, drivers in the post-tunnel zone have their attention reduced by 4.2% to 9.0%. Their reactions become slower, and ability to control vehicles decreases. The complex road alignment, such as curves and longitudinal slopes at the tunnel exit, can amplify the harm of the slack effect. Slack effect causes a delay of 80 m in the deceleration position before entering the curve, an increase of 5.7 km·h^-1 in the average speed of passing through the curve, a delay of 50 m in the track change position before entering the curve, and an increase of 7.1 cm in the trajectory offset of passing through the curve. It also brings a delay of 35 m in the acceleration distance after entering the longitudinal slope and an increase of 7.0 km·h^-1 in the average speed of passing through the longitudinal slope.