Joint Design of Fixed-Route and Paratransit Services with Autonomous Pods

Yan, Xiaoyu; Zheng, Hongyu; Dai, Tianxing; Nie, Yu (Marco) · 2025 · ROSA P / University of Michigan. Center for Connected and Automated Transportation

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Summary

This study addresses the financial and operational challenges of paratransit (PT) services, which consume a disproportionate share of transit budgets due to high labor costs and low ridership. Motivated by the potential of modular autonomous vehicles (pods) to reduce labor expenses and increase operational flexibility, the authors propose a joint design framework for fixed-route (FR) and PT services. The research aims to determine how a shared fleet of autonomous pods can be optimally allocated between these two services to minimize total user cost under a fixed budget, thereby preventing resource misallocation that could render either service dysfunctional. The authors develop a stylized mathematical model set in a square city with a grid road network. The FR service is modeled as a 2D grid system using pod-trains, while the PT service is modeled as an on-demand system operating in three modes: taxi, Dial-a-Ride, and ridesharing. The model utilizes workload transition networks to characterize PT operations and calculates agency costs (acquisition, distance, and time) and user costs (waiting, access, and in-vehicle time). The optimization problem seeks to minimize the sum of FR and PT user costs subject to a total budget constraint, determining optimal variables such as the number of FR lines, headways, pod-train sizes, and PT fleet sizes. A case study using empirical data from the Chicago region validates the model, comparing independent versus joint designs and analyzing the impacts of automation and modularity. The results indicate that joint design primarily prevents resource misallocation under tight budget constraints, though its ability to reduce total user cost is limited. Enforcing an equal-access constraint, which ensures PT users incur no greater cost than FR users, benefits PT riders at the expense of FR users, with negligible impact on total system cost. The study finds that modularity benefits FR operations by allowing the formation of efficient pod-trains, particularly when budgets are not strictly constrained. Conversely, automation yields greater improvements for PT users, whose cost structures are heavily driven by labor, making them more sensitive to efficiency gains, especially under tight budgets. Among PT modes, ridesharing proves the most flexible, accommodating a wide range of service levels based on available resources. The significance of this work lies in demonstrating how autonomous pod technology can integrate traditionally separate transit services, offering a pathway to more financially sustainable paratransit systems. By quantifying the distinct benefits of modularity for fixed routes and automation for paratransit, the study provides actionable insights for transit agencies aiming to optimize fleet allocation and improve service equity. The findings suggest that while joint design may not drastically lower total costs, it ensures system stability and fairness, highlighting the strategic value of flexible, autonomous fleets in addressing the high subsidy requirements of disability-accessible transportation.

Key finding

Joint design of fixed-route and paratransit services with autonomous pods prevents resource misallocation under budget constraints, with modularity benefiting fixed-route operations and automation providing greater efficiency gains for paratransit users.

Methodology

modeling

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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