首页|Understanding the effect of express services on passenger queuing and waiting times in a bus station using simulation
Understanding the effect of express services on passenger queuing and waiting times in a bus station using simulation
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NETL
NSTL
Elsevier
The "danger zone" phenomenon refers to a counterintuitive effect in public transport service planning, observed here in a simple corridor with an express service and an "all-stop" service, where increasing the express frequency (while holding all other conditions constant) can unexpectedly worsen system performance, leading to longer queues and increased total travel times (considering waiting and in-vehicle times). This study advances the understanding of this effect through three key contributions. First, it refines the analytical model by introducing explicit service-use categories (flexible express users, flexible all-stop users, and captive users) which improves clarity and strengthens the simulation framework. Second, it proposes and validates three key performance indicators (frequency amplitude, maximum waiting time, and severity) to quantify the impact of the danger zone and provide actionable tools for transit planners. Third, it develops a microsimulation model (DZ-SIM) that incorporates realistic station-level dynamics, passenger heterogeneity, and stochastic arrivals, offering insights into the conditions that exacerbate the danger zone and supporting future research. All simulation experiments are conducted over a realistic base scenario, which represents a congested corridor served by an all-stop and an express service. Across this fixed scenario, we test different assumptions regarding passenger behavior, bus and passenger arrival patterns, access to information, and system parameters. The simulation results validate the robustness of the danger zone effect: as express frequency increases, expected travel times initially rise (due to a sudden shift in demand toward the express service and the resulting congestion) and then stabilize at a plateau, offering no significant improvement until queues are fully dissipated. This nonmonotonic behavior reinforces the principle that only sufficiently large frequency increases yield meaningful improvements, supporting a "go big or go home" approach to express service planning. Our findings also reveal that the danger zone is most likely to occur when express services are highly attractive (i.e., offering significant time savings and serving a high proportion of flexible users) but are not frequent enough to accommodate the demand they generate. These insights support more effective express service planning by helping transit agencies avoid costly frequency increases that fail to deliver meaningful user benefits.
Public transportExpress servicesFrequency optimizationMicrosimulation
NETL
NSTL
Elsevier
