Transportation Optimization

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).

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
   [Link to Article] Abstract
   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
   [PDF]   [Link to Article] Abstract

   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.