Understanding the effect of express services on passenger queuing and waiting times in a bus station using simulation

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.