Impact of differences in vehicle type distribution across lanes on tunnel evacuation time
[Objective]Evacuation simulation is an important method for studying tunnel safety.Previous studies on highway tunnel evacuation simulation have assumed a uniform distribution of various vehicle types across each lane.However,this overlooks the potential impact of differences in vehicle type distribution across lanes(DVTDLs)and random vehicle distribution on evacuation time.In practice,different vehicle types tend to gravitate toward specific lanes,and the volumes as well as personnel loads vary significantly among these vehicles.We propose an algorithm for the random arrangement of vehicles within a tunnel,considering DVTDLs and random vehicle distribution.Concurrently,we develop a system with randomly arranging vehicle types(RAVT).[Methods]Our proposed method randomizes the arrangement of vehicles using parameters such as the spatial coordinates of the numerical model of the tunnel,vehicle sizes,vehicle model ratios,and vehicle type distribution differences.We apply this algorithmic process to develop the RAVT system.This system,based on HTML5,CSS,and JavaScript,can quickly calculate the parameters of vehicle arrangements and personnel loads and automatically generate the corresponding fire dynamics simulator(FDS)codes.This feature enables efficient and accurate vehicle arrangement in the numerical model of fire and evacuation of road tunnels.The FDS codes serve as a tool for modeling fires and can be directly imported into Pyrosim(a graphical tool integrated with FDS)and Pathfinder(a graphical tool for evacuation simulation).Using RAVT and Pathfinder,we established 12 scenarios featuring two-and three-lane tunnels as the subjects of our research.A total of 240 simulations were conducted.Our analysis focused on the effects of DVTDLs and random vehicle distribution on evacuation time under various conditions,ranging from extremely congested(vehicle spacing of 1.5 m),and normally congested(vehicle spacing of 5 m),to noncongested(vehicle spacing of 60 m).The lane model distribution ratios were set according to both uniformly and nonuniformly distributed proportions of each lane model,the latter being more reflective of real-world situations.[Results]The results reveal several key insights:(1)DVTDLs significantly affect evacuation time under extremely congested and normally congested conditions,with the mean difference of evacuation time reaching 43.51 s at the maximum.(2)Under noncongested conditions,DVTDLs have little effect on the average evacuation time.However,a uniform distribution of vehicle models across each lane increases the variability of evacuation times.(3)Large vehicles are likely to become stranded at the pedestrian crossing entrances,particularly in congested conditions and when vehicle types are uniformly distributed across lanes.This is especially true for large vehicles in overtaking lanes,leading to potential congestion during evacuation and,subsequently,longer evacuation times.(4)Given the same number of vehicles and vehicle type proportions,different vehicle distributions can cause significant differences in evacuation time.The maximum difference observed between the longest and shortest evacuation times was 59.76％.[Conclusions]By applying RAVT and Pathfinder software and analyzing the results,we have gained valuable insights into the effects of DVTDLs and random vehicle distribution on evacuation simulation results.We recommend that researchers and engineers consider these factors when conducting tunnel evacuation simulations.The algorithm and system developed in this study,along with the simulation method employed,provide a more scientifically robust reference for tunnel evacuation simulations.
highway tunnelvehicle type distribution across lanesrandom vehicle distributionevacuation simulation
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