I have done a bit of work on optimizing the design of transportation networks, mostly under the theme of usability. In a project funded by the U.S. Department of Transportation, we examined how to optimally retrofit a transportation network to make it more pedestrian-friendly (Rashidi et al., 2016). To accomplish this, we formulated an optimization model for optimally allocating limited resources to different traffic calming actions such as adding sidewalks and crosswalks. In another paper, we developed a model for designing a transportation network to make it more accessible to pedestrians (Li, Medal, and Qu, 2019).

Selected Publications

  1. Connected Infrastructure Network Design Under Additive Service Utilities
    Li, X. and Medal, H.. Connected Infrastructure Network Design Under Additive Service Utilities. Transportation Research Part B 120, 99–124.
    Publication Year: 2019-10-01 00:00:00
    [Link to Article] An infrastructure system usually contains a number of inter-connected infrastructure links that connect users to services or products. Where to locate these infrastructure links is a challenging problem that largely determines the efficiency and quality of the network. This paper studies a new location design problem that aims to maximize the total weighted benefits between users and multiple services that are measured by the amount of connectivity between users and links in the network. This problem is investigated from both analytical and computational points of view. First, analytical properties of special cases of the problem are described. Next, two integer programming model formulations are presented for the general problem. We also test intuitive heuristics including greedy and interchange algorithms, and find that the interchange algorithm efficiently yields near-optimum solutions. Finally, a set of numerical examples demonstrate the proposed models and reveal interesting managerial insights. In particular, we found that a more distance-dependent utility measure and a higher concentration of users help achieve a better total utility. As the population becomes increasingly concentrated, the optimal link design evolves from a linear path to a cluster of links around the population center. As the budget level increases, the installed links gradually sprawl from the population center towards the periphery, and in the case of multiple population centers, they grow and eventually merge into one connected component.
  2. Optimal traffic calming: A mixed-integer bi-level programming model for locating sidewalks and crosswalks in a multimodal transportation network to maximize pedestrians’ safety and network usability
    Eghbal Rashidi, Mohsen Parsafard, Hugh Medal, Xiaopeng Li. Transportation Research Part E: Logistics and Transportation Review, Volume 91, Pages 33–50
    Publication Year: 2016-01-20 00:00:00
    [PDF]   [Link to Article]

    We study the effect that installing sidewalks and crosswalks, as traffic calming facilities, has on the safety and usability of a transportation network with automobile, public transit and walking as modes of transportation. A mathematical programming model is proposed for this problem whose objective is to minimize the safety hazard for pedestrians and the total transportation cost of the network. We utilize a customized greedy heuristic and a simulated annealing algorithm for solving the problem. The computational results indicate that installing sidewalks and crosswalks at proper locations can reduce the overall transportation cost and improve pedestrians’ safety.

    3.

Funding

Optimizing the mobility and safety of walk-and-ride systems

Agency: National Center for Intermodal Transportation and Economic Competitiveness (funded by US Department of Transportation)Researchers: Medal, H.R. (PI) and Li, X.
Amount: $99,954 ($55,036 Medal share) with $102,988 cost share from Mississippi State University
Abstract:

In the project, we investigate the effect of traffic calming measures, such as crosswalks and sidewalks on the overall cost and safety of a multimodal transportation network system design. Our design problem includes auto, transit, and walking as modes of transportation. We propose a new method for multimodal user equilibrium (UE) traffic assignment with network reconstruction, which allows for mode switching. We propose a bi- level mathematical programming model that integrates multimodal user equilibrium traffic assignment in the lower level and the network design in the upper level. The model tries to optimally implement and locate sidewalks and crosswalks considering limited financial resources to provide city planners with a comprehensive tool for planning. Due to the complexity of the problem, it requires a large amount of computational resources and therefore cannot be solved efficiently for large scale problems using state of the art solvers; hence we develop a greedy heuristic and a simulated annealing algorithm to solve large problems. The algorithms use a nonlinear complimentary algorithm to solve the UE traffic assignment. The computational results show that implementing sidewalks and crosswalks both reduces the overall transportation cost and improves pedestrians’ safety.

Mississippi transportation infrastructure improvement opportunities

From the Hearin Foundation (through the Mississippi Economic Council)

Researchers: Li, X., Breen, D., French, E., Medal, H.R. (Co-PI)

Amount: $225,000 ($57,500 Medal share)

Abstract: This project aims to identify strategies and policies that will ensure that an adequate level of resources will be available to address the transportation infrastructure funding gap that undermines economic development and job creation in the state of Mississippi. Research activities conducted with funding for this project include:

  • Assessment of the current transportation infrastructure performance in the state of Mississippi
  • Identification of opportunities to improve the current transportation infrastructure
  • Study and development of new funding mechanisms, to include potential public-private ventures
  • Synergy between activities funded under this project and ongoing work of Mississippi State University’s National Center for Intermodal Transportation for Economic Competitiveness
  • Comparison and evaluation of alternative state policies for reducing transportation funding gaps and identification of alternative realistic strategies, policies, and funding mechanisms that are required to meet the future revenue demands to fund transportation infrastructure in the state of Mississippi
  • Identification of projects that represent opportunities for improvement to the current infrastructure
  • Examination and prioritization of projects, innovative strategies, policies, and funding mechanisms linked to cluster-related multimodal investments that focus on the targeted industries identified in Blueprint Mississippi and Mississippi employment centers