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arXiv · 2508.18643

Hierarchical Pod Routing for Modular Transit Systems

Tina Radvand·Alireza Talebpour·Yanfeng Ouyang
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Abstract

Modular bus systems allow fixed-route transit services to better match vehicle capacity to passenger loads. Operating modular bus systems requires deciding how pods are assigned to scheduled services, repositioned for subsequent assignments, and parked when not in service. A time-space minimum-cost flow formulation provides an exact benchmark for this problem, but it does not scale well to large urban transit systems with many pod-level routing decisions. This paper proposes a Hierarchical Pod Routing (HPR) framework that solves the problem in two stages. The first stage uses a minimum path-cover formulation to assign service trips to pods while minimizing fleet size. The second stage determines how pods are repositioned and parked between consecutive assignments to minimize empty movement and parking costs. The proposed method is evaluated on benchmark instances constructed from New York City MTA GTFS data, which capture realistic bus schedules and passenger-demand patterns. The results show that HPR remains within $8\%$ of the exact minimum-cost flow objective on the largest instances, while achieving more than a four order of magnitude reduction in runtime and an approximately one order of magnitude reduction in memory use. The results also show that HPR distributes service trips more evenly across pods and reduces the frequency of long idle periods between assignments, while the exact minimum-cost flow formulation produces shorter distances between consecutive assignments. Sensitivity analyses further show that HPR maintains consistent performance across a range of operating-cost assumptions. These findings suggest that HPR can provide a scalable and near-optimal planning approach for modular transit systems.

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BibTeXRIS

Tina Radvand, Alireza Talebpour, Yanfeng Ouyang. 2026-09-18. Hierarchical Pod Routing for Modular Transit Systems. https://arxiv.org/abs/2508.18643

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