Bilevel subsidy-enabled mobility hub network design with perturbed utility coalitional choice-based assignment
For urban mobility planners and policymakers, this work provides a computationally tractable bilevel model to design subsidy schemes for mobility hub networks, though the approach is incremental as it combines existing bilevel optimization with a known route choice model.
This paper develops a bilevel optimization model for mobility hub network design, where the platform sets subsidies to influence last-mile operators and travelers. The method achieves sub-1% optimality gaps in minutes on a real-world Long Island Rail Road case with 244 nodes, enabling policymakers to quantify the social surplus value of mobility hubs.
Urban mobility is undergoing rapid transformation with the emergence of new services. Mobility hubs (MHs) have been proposed as physical-digital convergence points, offering a range of public and private mobility options in close proximity. By supporting Mobility-as-a-Service, these hubs can serve as focal points where travel decisions intersect with operator strategies. We develop a bilevel MH platform design model that treats MHs as control levers. The upper level (platform) maximizes revenue or flow by setting subsidies to incentivize last-mile operators; the lower level captures joint traveler-operator decisions with a link-based Perturbed Utility Route Choice (PURC) assignment, yielding a strictly convex quadratic program. We reformulate the bilevel problem to a single-level program via the KKT conditions of the lower level and solve it with a gap-penalty method and an iterative warm-start scheme that exploits the computationally cheap lower-level problem. Numerical experiments on a toy network and a Long Island Rail Road (LIRR) case (244 nodes, 469 links, 78 ODs) show that the method attains sub-1% optimality gaps in minutes. In the base LIRR case, the model allows policymakers to quantify the social surplus value of a MH, or the value of enabling subsidy or regulating the microtransit operator's pricing. Comparing link-based subsidies to hub-based subsidies, the latter is computationally more expensive but offers an easier mechanism for comparison and control.