Research on Calculation of Warning Zone Length of Freeway Based on Micro-Simulation Model

The traditional calculation method can only determine the minimum length of the warning zone. In this paper, it proposes a method to determine the length of freeway warning zone using VISSIM simulation model and surrogate safety assessment model (SSAM). The simulation model of freeway maintenance work zones is constructed based on VISSIM, and calibrates the VISSIM simulation model. Through improving the time to collision (TTC) model, the traffic conflict discrimination threshold of the freeway maintenance work zone was determined. Based on the average absolute percentage error (MAPE) of traffic conflict, the validity of VISSIM simulation model and threshold are verified. Meanwhile, the SSAM is used to determine the changing trend of the number of traffic conflicts; a linear regression model is established to analyze the relationship between simulated and observed traffic conflicts. In addition, under different traffic conditions, the relationship between travel time, delay, traffic conflict and the warning zone length is analyzed. Based on traffic conflict number and safety evaluation index, the optimal length of warning zone is determined, and the relationship between warning zone length and safety evaluation index is studied. The results show that the simulated traffic conflict is reasonable consistent with the observed traffic conflict; under different traffic conditions, travel time and delay increase slowly with the increase of warning zone length; traffic conflicts decrease with the increase of warning zone length, when the warning zone length is more than 2200 m, traffic conflicts show a certain convergence state; When the warning zone length is 2200m, the number of traffic conflicts, delay and safety evaluation index are the minimum, and the safety is the best. Therefore, the method can determine the optimal length of the warning area and improve the safety of the warning zone.