All posts by yni957

Recent research

A-PASS for Travel Demand Management

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Auction-Based Permit Allocation and Sharing System (A-Pass) for Travel Demand Management, co-authored by Ruijie Li and Xiaobo Liu (both at Southwest Jiaotong University, China).

This is a follow up to another paper related to the mechanism design problems arising from ridesharing.  In this paper, we try to show the promise of integrating ridesharing with quantity-based travel demand management.  One of the main insights is that by auctioning out permits (e.g., to use a road facility), we can eliminate the deficits that are otherwise unavoidable in classical  Vickrey-Clark-Gloves mechanism.  The paper just came out in Transportation Science. You may read the abstract below and download a preprint here.

We propose a novel quantity-based demand management system aiming to promote ride-sharing. The system sells the permit to access a facility (conceptualized as a bottleneck) by auction but encourages commuters to share the permits with each other. The permit is classified according to access time and the commuters may be assigned one of the three roles: solo driver, ride-sharing driver, or rider. At the core of this auction-based permit allocation and sharing system (A-PASS) is a trilateral matching problem (TMP) that matches permits, drivers and riders. We formulate TMP as an integer program, and prove it can be reduced to an equivalent linear program. A pricing policy based on the classical Vickrey-Clark-Gloves (VCG) mechanism is proposed to determine the payment for each commuter. We prove, under the VCG policy, different commuters will pay exactly the same price as long as their role and access time are the same. We also show A-PASS can eliminate any deficit that may arise from the VCG policy by controlling the number of shared rides. Results of numerical experiment suggest A-PASS strongly promote rider-sharing. As ride-sharing increases, all stake holders are better off: the ride-sharing platform receives greater profits, the commuters enjoy higher utility, and the society benefits from more efficient utilization of infrastructure.

Recent research

A Physical Model of Street Ride-Hail

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The work was initiated by my former student, Hongyu Chen, as part of his PhD research.  He wanted to build a “physical model” of street-hail taxi matching that can be calibrated and validated with real data (taxi trajectory).  This is very difficult because passenger wait time cannot be directly observed in taxi trajectory data. Hongyu came up with a rather clever and elaborated method to accomplish just that. Read the abstract below and download the paper here.

In this study, we show that the passenger-driver matching process in street ride-hail is dictated by the physical limitation of a passenger’s average eyesight and the preference of cruising taxi drivers for certain locations. Together, these two spatiotemporal features, called effective hail distance (EHD) and local area attractiveness (LAA) respectively, define the number of vacant taxis that a passenger can reach, and accordingly the distribution of her waiting time. To calibrate the waiting time distribution, we extract maximum possible waiting times from taxis GPS trajectory data, by tracking the movements of vacant taxis cruising around a pickup location. Then we prove that, for a given EHD, the extracted maximum possible waiting time follows the same distribution as passenger waiting time. The proposed matching mechanism, along with the novel calibration method, leads to a general model of street ride-hail that can produce reliable estimates of passenger waiting time under a wide variety of market conditions. Moreover, the matching process in the phone-based ride-hail is shown to be a special case of the proposed model, when EHD approaches infinity. This result lays the foundation for understanding and comparing the performance of ride-hail services. It can also help address regulatory and operational questions facing key stake holders in this industry.

housekeeping

My first post

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I finally decided that I need a research+blog type place to share my work and writing.   My student told me  Northwestern provides a web-hosting service based on WordPress.  I have a few hours to spare since it is a MLK day. The tool seems quite reasonable and hence I took the plunge.  Let’s see how it goes…