Impact of Modularized Autonomous Vehicles on Transit System Design and Operations

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

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Summary

This study investigates the operational and design implications of integrating fixed-route (FR) transit and paratransit (PT) services using a shared fleet of modular autonomous vehicles (pods). The research is motivated by the high subsidy costs of PT services, which consume a disproportionate share of transit budgets, and the potential for automation and modularity to improve efficiency. While FR and PT services are traditionally operated separately, the authors propose a joint design model where a single operator allocates a homogeneous fleet of pods between the two services to minimize total user cost under a fixed budget. The authors developed a stylized mathematical model set in a square city with a grid road network. The FR service utilizes pod-trains (linked pods) operating on a 2D grid, while the PT service operates as an on-demand system using individual pods. The PT service was modeled in three modes: taxi, Dial-a-Ride, and ridesharing, with the latter analyzed through workload transition networks to account for assignment, pickup, and drop-off dynamics. The model accounts for agency costs (acquisition, distance, and time) and user costs (waiting, access, and in-vehicle time). A case study was conducted using empirical data from the Chicago region to evaluate independent versus joint designs, testing various pod sizes, automation levels, and budget constraints. The results indicate that joint design primarily prevents resource misallocation that could render a service dysfunctional under tight budgets, 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 riders without significantly altering total system costs. Modularity benefits FR operations by allowing small pods to form trains, improving efficiency when budgets are not strictly constrained. Conversely, automation yields greater improvements for PT users, whose labor-intensive cost structure makes them more sensitive to efficiency gains, particularly under tight budgets. Among PT modes, ridesharing proved the most flexible, allowing for a wide range of service levels based on available budget. The study concludes that while joint design offers stability and prevents service failure, the distinct operational characteristics of FR and PT services mean that technological benefits are not uniformly distributed. Modularity enhances FR efficiency through aerodynamic and capacity benefits, whereas automation is critical for reducing the high labor costs associated with PT. The findings suggest that transit agencies should consider joint fleet management to ensure equitable service provision, but must recognize that the primary efficiency gains from autonomous pods will likely accrue to the paratransit sector due to its current cost structure.

Key finding

Joint design of fixed-route and paratransit services using modular autonomous vehicles prevents resource misallocation under budget constraints, with modularity benefiting fixed-route operations and automation disproportionately improving paratransit efficiency.

Methodology

modeling

Provenance

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

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