CEAE Faculty Candidate Speaker Lindsay Graff: Optimizing Mobility Infrastructure, Services, and Subsidies in Multimodal Transportation Networks

Cities aiming to improve their transportation networks are integrating emerging mobility options at a rapid pace. These modes provide commuters with greater flexibility to construct more convenient trips and reach a larger set of essential service destinations. However, existing network models and methods do not sufficiently capture the full set of travel mode combinations and travel cost factors perceived by individual travelers. To this end, we introduce NOMAD: 
Network Optimization for Multimodal Accessibility Decision-making. NOMAD integrates the personal vehicle, transportation network company, carshare, public transit, personal bike, bikeshare, scooter, walking, and feeder micro-transit modes into a unified routable network model. Its open-source implementation can be used to inform policy development in transportation networks with shared mobility. Two policies of interest are the provision of need-based mobility subsidies and the coordinated design of a multimodal transportation network. For the mobility subsidy allocation problem, we propose a mixed-integer linear program that assigns subsidies based on an individual’s geographic residence. The optimization model maximizes accessibility to jobs while ensuring a fair allocation, and findings from a case study in Pittsburgh suggest that mobility subsidies can serve to compensate communities with inferior transit service and network infrastructure. For the multimodal transportation network design problem, we propose a bi-level optimization model to determine the location of bikeshare stations and microtransit service zones. The model maximizes accessibility and fairness metrics, and preliminary results indicate a balanced distribution of proposed transportation investments across different neighborhoods. The talk concludes with opportunities for future work related to decision-making in networked systems, including the optimal design of complete streets and rail capacity expansion.