Efficiency paradox and robustness of elevator-assisted evacuation in a deeply buried subway station

In deeply buried subway stations, passengers using stairs and escalators need to walk a long vertical distance to reach the ground, which leads to prolonged evacuation times. On the contrast, elevators can vertically transport passengers directly to the ground. This study aims to study the evacuation efficiency after adding an elevator exit during daily commutes under varying buried depths and passenger flows. For this purpose, models for elevator scheduling and the subway station were developed. Three types of simulation scenarios were set up. Scenario A analyzed the baseline condition without elevator exits. Scenario B incorporated varying proportions of passengers opting for the elevator exit. Scenario C examined the combined effects of route-changing behavior alongside variations in elevator capacity and operating speed. The acceptable queue size was considered to reflect the psychology of passengers who change evacuation routes. An evacuation time ratio (ETR) was used to analyze evacuation efficiency quantitatively. It turns out that adding an evacuation elevator without proper allocation of passengers to evacuation routes can result in the evacuation efficiency paradox (EEP). To avoid EEP, the robustness of evacuation efficiency was analyzed. Results show that directing passengers to optimize their evacuation routes is more effective for improving overall efficiency than merely increasing elevator capacity and speed. When an acceptable queue size is under 30 passengers, evacuation efficiency improves by 15 % across all depths, with greater gains at shallower depths. Taking construction and operating costs into consideration, it is better to maintain a proper queue size and select an elevator with around 15-passenger capacity and 1–2 m/s speed. When a subway station is deeply buried or higher evacuation efficiency is required, increasing the elevator’s rated capacity and speed becomes necessary. This paper can provide novel ideas for the control strategy of large passenger flow and offer guidance on the design of elevator exits in deeply buried stations.