Optimal Warning Distance for Expressway Construction Area under Mixed Traffic Flow

To alleviate the sharp decline in traffic efficiency caused by reduced number of lanes or the presence of obstacles and reduce the risk of accidents due to frequent lane changes or acceleration and deceleration in expressway operation area, taking the Wufengshan north-south 4-lane river crossing channel in Jiangsu Province as the research environment, the related research on typical operation area of expressway is conducted, a comprehensive indicator system for efficiency, safety and fuel consumption in expressway operation area is constructed. Based on Vissim simulation software, considering different traffic volumes, assembly rates and warning distance conditions, the road scenario and warning model are created. The optimal warning distance for vehicles under different conditions in expressway operation area is studied by using Bayesian neural network for prediction. The result shows that the average relative errors of this method for predicting the comprehensive, safety and energy consumption indicators of expressway operation area are 0.4%, 0.4% and 0.2% respectively. Through the analysis of the optimal warning distance for comprehensive efficiency, safety and energy consumption indicators, it is concluded that (1) higher assembly rates lead to better result in all the 3 indicators, and the optimal warning distance becomes shorter; (2) under free flow condition, the optimal warning distance is 300-800 m and it increases with the increase of traffic volume; (3) under saturated traffic flow condition, the optimal warning distance is 800-1 200 m, but the increase in traffic volume at this time has little influence on the warning distance; (4) after traffic volume is oversaturated, the optimal warning distance is 1 200-1 800 m, and it continues to increase as the traffic volume increases. The research result can provide some reference for the safe driving of vehicles in expressway operation area and the issuance of road warning by traffic management departments, and also provide a method for predicting the optimal distance of vehicle warning in expressway operation areas.