Abstract:

Selecting between fixed-route and flexible-route bus systems is a critical strategy for improving the operational efficiency of urban public transit. While most existing studies focus primarily on passenger demand, this study adopts a more comprehensive perspective by incorporating demand intensity, service area size, and block size. Based on the cost structures of both fixed- and flexible-route systems, mathematical models are developed to determine the optimal vehicle capacities and departure intervals that minimize total system costs. Closed-form solutions for these optimal values are derived for both transit modes. In addition, the study identifies the conditions under which each system is preferable, and derives threshold formulas for demand intensity, service area size, and block size. Research demonstrates that the operating costs of flexible bus systems (particularly pickup/drop-off costs) and passenger walking costs in fixed-route systems are pivotal determinants in transit mode selection. These cost factors exhibit threshold-dependent effects: only when their quantitative relationship meets specific conditions do demand intensity, service area scale, and block size significantly influence mode choice. Numerical simulations validate the proposed mode selection methodology between flexible and fixed-route bus systems. The findings provide actionable decision support for real-world transit planning applications.

Key words: transit mode selection, fixed transit, flexible transit, demand intensity, service area size, block size