Abstract:  Existing tunnel evacuation simulation studies generally assume fully loaded vehicles, ignoring the impact of actual passenger loading on evacuation time. To measure the passenger loading characteristics of road vehicles, this study proposes and defines the concept of “passenger load factor”, which refers to the ratio of the total actual passenger volume of all vehicles in the study area to the total rated passenger capacity within the statistical period. Statistics of 3 260 vehicles show that the actual passenger load factor is 27.66%. Taking a typical underwater shield tunnel as an example, 48 evacuation scenarios are simulated using Pathfinder. The actual passenger load factor (27.66%) and five graded passenger load factor levels (100%, 80%, 60%, 40%, and 20%) are set, combined with different numbers of lanes and vehicle spacing conditions, to analyze the impact of passenger load factor variation on evacuation time. The results show that: (1) Passenger load factor variation has a considerable impact on evacuation time in underwater shield tunnels. Simulation results assuming full load yield remarkably overestimated evacuation time. When the passenger load factor rises from the actual 27.66% to 100%, evacuation time increases by as much as 217.03%. (2) Evacuation time exhibits a strong positive linear correlation with passenger load factor (R²>0.95). Accordingly, linear regression models describing the relationship between passenger load factor and evacuation time under different numbers of lanes and vehicle spacings are established. (3) Both vehicle spacing and the number of lanes affect the degree of influence of passenger load factor on evacuation time and accelerate the growth rate of evacuation time with the increase of passenger load factor. Moreover, an interaction effect exists between the two factors: more lanes and smaller spacing will strengthen the prolongation effect of passenger load factor on evacuation time. These findings suggest that the impact of passenger load factor variation be considered in tunnel evacuation simulation studies and the actual passenger load factor value of 27.66% can be referenced to improve the accuracy and reliability of simulation results.

Key words: underwater shield tunnels, passenger load factor, field investigation, evacuation simulation, evacuation time