Student Seminar by Mr. Yuan Liang on Apr 28, 2026, 2:00PM

Title: Air Pollution and Urban Mobility: Two Quasi-experimental Designs

Speaker: Mr. Yuan Liang (Department of Geography, Hong Kong Baptist University)

Date: Apr 20, 2026 (Monday)

Time: 2:00 pm - 3:00 pm

Venue: Room 1010, CLL, Department of Geography, 10/F, The Jokey Club Tower, The University of Hong Kong

Registration Link: https://forms.cloud.microsoft/r/L6i8Kxxf2D

ITS Student Committee will provide a beverage for registered participants.

Abstract: I will share two studies that employ quasi-experimental designs to explore the bidirectional causal link between air pollution and urban mobility in urban China. The first study uses thermal inversion, a meteorological phenomenon, as an instrumental variable for air pollution to estimate the causal effect of air pollution on dockless bike-sharing usage. The second applies a difference-in-differences approach to evaluate the causal impact of fare-free public transport on air quality. The findings offer insights into the societal impacts of air pollution through the lens of urban mobility and hold implications for sustainable urban transport policies.

Bios: Yuan Liang is a Ph.D. candidate in the Department of Geography at Hong Kong Baptist University and a former visiting student in the Transport Studies Unit at the University of Oxford. His current research uses causal evidence to explore the linkages between climate change, air pollution, and urban mobility. His work has been published in Transportation Research Part A/D/E, Transportation, and Environmental Research Letters.

Student Seminar by Mr. Kaihang Zhang on Apr 20, 2026, 4:00PM

Title: Let Drivers Roam: How ETA Slack Unlocks Network Effects in On-Demand Food Delivery Markets

Speaker: Mr. Kaihang Zhang (Department of Civil Engineering)

Date: Apr 20, 2026 (Monday)

Time: 4:00 pm - 5:00 pm

Venue: Room 8-28, Haking Wong Building, The University of Hong Kong

Registration Link: https://forms.cloud.microsoft/r/bMhERMSx61

ITS Student Committee will provide a beverage for registered participants.

Abstract: Platforms in on-demand delivery compete on speed by committing to tight estimated time of arrival (ETA) targets. Tight ETAs reduce drivers’ flexibility while busy, limiting order bundling and cross-neighborhood switching; this fragments the implicit service network and restricts pooling benefits. We develop a parsimonious steady-state model that links an ETA commitment to endogenous bundling, routing and repositioning workload for multi-stop tours, and a switching probability that captures whether drivers can relocate to adjacent restaurant clusters between bundles. These endogenous variables feed into a mean-field (aggregate level) queuing approximation for pooled matching, yielding tractable expressions for assignment-delay metrics. Within an operating range we call the active regime, relaxing ETA commitments increases bundling and the probability that a busy driver can accept a new assignment, reduces per-order service time, and lowers assignment delay. We show that tight ETAs fragment the cluster network, loosing pooling benefits. We then introduce a fleet-based price of urgency that quantifies the additional fleet required to meet a target assignment delay when operating at tighter ETAs relative to a benchmark, highlighting a nonlinear fleet cost near the connectivity threshold where switching becomes insufficient to maintain network connectivity.

Bios: Kaihang is a PhD student at the Department of Civil Engineering, HKU, supported by HKPF and HKUPS. His research interests include modeling of complex systems, optimization under equilibrium constraints, and behavioral analysis and operations. Prior to HKU, he worked on traffic state analysis and public transportation system design. He holds bachelor’s degrees from ZJU and UIUC, and a master’s degree from UC Berkeley.

Student Seminar by Mr. Yuzhen Feng on Mar 26, 2026, 3:30PM

Title: Resource-Constrained User Equilibrium

Speaker: Mr. Yuzhen Feng (The Hong Kong Polytechnic University)

Date: Mar 26, 2026 (Thursday)

Time: 3:30 pm - 4:30 pm

Venue: Room 8-28, Haking Wong Building, The University of Hong Kong

Registration Link: https://forms.cloud.microsoft/r/552KT3frUg

ITS Student Committee will provide a beverage for registered participants.

Abstract: We study user equilibrium with resource constraints (UERC) where users face strict budget on energy, time, risk, etc., motivated by applications in urban mobility, perishable logistics, and itinerary planning. UERC unifies user equilibrium and the resource‑constrained shortest path problem by allowing both travel costs and resource consumption to depend on congestion, making path feasibility endogenous. We formulate UERC as a quasi‑variational inequality and prove that a UERC exists when every user has at least one feasible path regardless of congestion; otherwise, deciding existence is NP-hard. We establish uniqueness in networks with parallel links between a single origin-destination pair, even with heterogeneous budgets among users, and show counterexamples where minimal generalizations destroy uniqueness. When cost equals resource consumption on every link, UERC coincides with classical user equilibrium and thus inherits its uniqueness of link flows. When cost and resource consumption differ but their ratio is uniformly bounded above and below, both the price of anarchy and unfairness (the max-to-min ratio of equilibrium costs experienced by the same user type) are bounded; without such comparability, both can be unbounded. We also reveal a paradoxical comparative statics: increasing users' budgets can raise total system cost by allowing more users to already congested routes. Computationally, we develop a penalty‑based algorithm with column generation that repeatedly solves a resource‑constrained shortest path subproblem, and prove convergence under the same sufficient condition for existence. Experiments on benchmark road networks demonstrate the computational scalability of our algorithm and quantify the impact of endogenous feasibility on equilibrium outcomes.

Bios: Mr. Yuzhen Feng is currently a third-year Ph.D. student in Transportation at The Hong Kong Polytechnic University, supervised by Dr. Wei Liu. His recent work is mainly related to transportation network modeling, optimization, and equilibrium. He received his B.Mgt. degree in Information Management and Information System from the School of Economics and Management at Tongji University in 2023. During his undergraduate studies, he also worked with Prof. Xiaolei Wang on dynamic en-route ride-pooling. He is a recipient of the Hong Kong Ph.D. Fellowship.