Characteristics of Mixed Traffic Flow in Highway Tunnels as Affected by Changes in Illumination

In a mixed traffic flow environment, the tunnel entrance and exit sections are prone to changes in traffic flow characteristics due to differences in illumination and the complexity of vehicle-following behavior. To investigate the characteristics of mixed traffic flow at tunnel entrances and exits affected by changes in illumination, a car-following model for human-driven vehicles (HDVs) was constructed based on actual vehicle tests and fuzzy controllers. Considering the degradation phenomenon of intelligent connected vehicles (ICVs), an ICVs car-following model was constructed. Finally, a mixed traffic flow model based on cellular automata and actor-critic (AC) algorithms was constructed. Through simulation, the characteristics of the impact of illumination on mixed traffic flow at the entrance and exit sections under different ICVs penetration rates were analyzed and evaluated in terms of traffic efficiency and stability. The results show that the illumination value changes drastically at the tunnel entrance, and the illumination value inside the tunnel fluctuates between 5 and 10 lx; under the influence of illumination change, the speed of vehicles at the tunnel entrance decreases and the following distance increases, and the speed of vehicles in the middle of the tunnel and the following distance are relatively smooth; when the penetration rate of ICVs in the mixed traffic flow inside the tunnel reaches 100%, the maximum flow rate of the traffic flow is improved by 1.4 times, and the standard deviation of the speed of the vehicles is positively correlated to the penetration rate of the ICVs. The standard deviation of vehicle speed is positively correlated with the penetration rate of ICVs, which is reduced by 85.45%. ICVs reduce the influence of illuminance on the traffic flow, and effectively reduce the speed fluctuation of the vehicle at the entrance and exit; it can be seen that the participation of ICVs significantly improves the average speed and the maximum flow of the traffic flow, reduces the speed fluctuation of the traffic flow, and also significantly improves the safety of the traffic flow under the condition of high penetration rate.