Xiaotong Sun

Xiaotong Sun

Xiaotong Sun is an assistant professor in the Intelligent Transportation Thrust at HKUST(GZ)

Publications

You can also find my articles on my Google Scholar profile.

Journal Articles

Static-to-dynamic modeling of the coupled mobility-as-a-service subscriptions and travel choices

Published in TRANSPORTATION RESEARCH PART C:Emerging Technologies, 2026

A distinguishing feature of the emerging Mobility-as-a-Service (MaaS) is the provision of integrated mobility services through subscription plans, commonly known as MaaS bundles. While its intertemporal and multi-modal tariff structure creates a close coupling between periodic subscription decisions and daily travel choices, theoretical analyses remain limited in the interplay between periodic bundle subscriptions and daily path choices. This study addresses this gap by examining how these intertwined travel behaviors influence system evolution, stability, and overall performance under MaaS’s two-part tariff structure. We first develop a hierarchical discrete choice model that incorporates travelers’ heterogeneous loyalty to MaaS bundles to characterize the static equilibrium, formulated as a variational inequality problem. We then represent the dynamic evolution of subscriptions and path choices through a two-level day-to-day dynamical model that embeds both path inertia and bundle loyalty, and we derive the corresponding separate sufficient and necessary stability conditions. Both theoretical and numerical convergence analyses reveal that daily path inertia dominates the convergence of the coupled dynamics, outweighing the influence of bundle loyalty. We further introduce a bundle-pricing framework under a two-part tariff structure that links travelers’ choices with system performance and supports evaluating trade-offs across policy objectives. Finally, static optimal bundle pricing, which is computationally less demanding than dynamically optimizing bundle prices, also demonstrates robust performance in dynamic scenarios.

Recommended citation: Pan, M., Sun, X., Mo, H. (2026). Static-to-dynamic modeling of the coupled mobility-as-a-service subscriptions and travel choices. Transportation Research Part C: Emerging Technologies, 191, 105847.
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Substitution or complement? Uncovering the interplay between ride-hailing services and public transit

Published in TRANSPORTATION RESEARCH PART C:Emerging Technologies, 2026

The literature on transportation network companies (TNCs), also known as ride-hailing services, has often characterized these service providers as predominantly substitutive to public transit (PT). However, as TNC markets expand and mature, the complementary and substitutive relationships with PT may shift. To explore whether such a transformation is occurring, this study collected travel data from 96,716 ride-hailing vehicles during September 2022 in Shanghai, a city characterized by an increasingly saturated TNC market. An enhanced data-driven framework is proposed to classify TNC-PT relationships into four types: first-mile complementary, last-mile complementary, substitutive, and independent. Using baseline parameter settings, our findings reveal a substantial increase in the complementary ratio (9.22%) and a relative decline in the substitutive ratio (9.06%) compared to previous studies. Furthermore, to examine the nonlinear impact of various influential factors on these ratios, a machine learning method integrating categorical boosting (CatBoost) and Shapley additive explanations (SHAP) is proposed. The results show significant nonlinear effects in some variables, including the distance to the nearest metro station and the density of bus stops. Moreover, metro hubs and regular single-line stations exhibit distinct effects on first- or last-mile complementary ratios. These ratios’ relation to the distance to single-line stations shows an inverted U-shaped pattern, with effects rising sharply within 1.5 km, remaining at the peak between 1.5 and 3 km, and then declining as the distance increases to about 15 km. On the other hand, the distance to multi-line hubs initially maintains a positive influence on the complementary ratios within 9 km, which then stabilizes in the 9–18 km range. These findings offer valuable insights for policymakers to promote urban multimodal mobility systems integrating ride-hailing and public transit.

Recommended citation: Jin, Z., Sun, X., Zhen, L., Gu, W., & Tu, H. (2026). Substitution or complement? Uncovering the interplay between ride-hailing services and public transit. Transportation Research Part C: Emerging Technologies, 189, 105747.
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On the robotic uncertainty of fully autonomous traffic: From stochastic car-following to mobility–safety trade-offs

Published in TRANSPORTATION RESEARCH PART C:Emerging Technologies, 2025

This paper presents an analytical model framework that delineates the endogenous reciprocity between traffic safety and mobility that arises from AVs’ robotic uncertainties. Using both realistic car-following data and a stochastic intelligent driving model (IDM), the stochastic car-following distance is derived as a key parameter, enabling analysis of single-lane capacity and collision probability. A semiMarkov process is then employed to model the dynamics of the lane capacity, and the resulting collision-inclusive capacity, representing expected lane capacity under stationary conditions, serves as the primary performance metric for fully autonomous traffic. The analytical results are further utilized to investigate the impacts of critical parameters in AV and roadway designs on traffic performance, as well as the properties of optimal speed and headway under mobilitytargeted or safety-dominated management objectives.

Recommended citation: Li, H., Sun, X., Zhuang, C., & Li, X. (2025). On the robotic uncertainty of fully autonomous traffic: From stochastic car-following to mobility–safety trade-offs. Transportation Research Part C: Emerging Technologies, 178, 105254.
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Planning of truck platooning for road-network capacitated vehicle routing problem

Published in TRANSPORTATION RESEARCH PART E-LOGISTICS AND TRANSPORTATION REVIEW, 2025

This study pioneers the integration of truck platooning into capacitated vehicle routing problems with time windows (CVRPTW) by developing a road network-based optimization framework and a three-stage algorithm to minimize total costs—including dispatch and energy expenses—while serving multi-customer demands, with numerical experiments validating the model’s efficacy and quantifying platooning’s cost-saving potential in real-world logistics operations.

Recommended citation: Hao, Y., Chen, Z., Sun, X., & Tong, L. (2025). Planning of truck platooning for road-network capacitated vehicle routing problem. Transportation Research Part E: Logistics and Transportation Review, 194, 103898.

Hierarchical prediction uncertainty-aware motion planning for autonomous driving in lane-changing scenarios

Published in TRANSPORTATION RESEARCH PART C-EMERGING TECHNOLOGIES, 2025

This study evaluates the energy-saving benefits of truck platooning across the US national highway freight network by integrating aerodynamic modeling with large-scale traffic simulations, revealing significant fuel efficiency gains and reduced emissions through optimized inter-vehicle coordination, validated via real-world freight corridor data.

Recommended citation: Yao, R., & Sun, X. (2025). Hierarchical prediction uncertainty-aware motion planning for autonomous driving in lane-changing scenarios. Transportation Research Part C: Emerging Technologies, 171, 104962.

A data-driven approach to uncovering the charging demand of electrified ride-hailing services

Published in TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT, 2025

This study analyzes the distinct charging demand patterns of electric ride-hailing vehicles using trip data from 96,716 Shanghai-based vehicles, employs spatial regression models to reveal significant correlations between charging needs and built environment variables, and integrates supply-side data to evaluate public charging infrastructure sufficiency, uncovering spatiotemporal demand variations and spatial lag effects.

Recommended citation: Jin, Z., Sun, X., Xu, Z., & Tu, H. (2025). A data-driven approach to uncovering the charging demand of electrified ride-hailing services. Transportation Research Part D: Transport and Environment, 139, 104599.

Economic Analysis of On-Street Parking with Urban Delivery

Published in TRANSPORTATION SCIENCE, 2024

This study examines the impact of delivery-driven curb parking demands on urban curb dynamics through continuum modeling and comparative statics, revealing that optimized metered parking pricing for general users outperforms dedicated delivery bays and duration caps, with demand source-dependent strategies and adaptive bay sizing proving critical to curb management efficiency, thereby challenging the necessity of delivery-specific infrastructure under optimal pricing.

Recommended citation: Xu, Z., & Sun, X. (2024). Economic Analysis of On-Street Parking with Urban Delivery. Transportation Science, 58(6), 1300-1318.

Hub-Based Platoon Formation: Optimal Release Policies and Approximate Solutions

Published in IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS, 2024

This study optimizes truck platoon formation at highway hubs under decentralized, distributed, and centralized policies by developing dynamic programming-driven release thresholds and receding horizon solutions, revealing that decentralized strategies—despite yielding ~3.5% and 8% lower rewards than distributed and centralized approaches—achieve near-optimal performance without inter-hub coordination, validated via simulations on Swedish highway hubs.

Recommended citation: Johansson, A., Nekouei, E., Sun, X., Johansson, K. H., & Mårtensson, J. (2023). Hub-based platoon formation: Optimal release policies and approximate solutions. IEEE Transactions on Intelligent Transportation Systems, 25(6), 5755-5766.

Investigating the Potential of Truck Platooning for Energy Savings: Empirical Study of the US National Highway Freight Network

Published in Transportation Research Record, 2021

This paper investigates the potential of truck platooning for energy savings in the US national highway freight network.

Recommended citation: Sun, X., Wu, H., Abdolmaleki, M., Yin, Y*., & Zou, B. (2021). "Investigating the Potential of Truck Platooning for Energy Savings: Empirical Study of the US National Highway Freight Network." Transportation Research Record, 03611981211031231. [TRR][PDF(pre-print)]
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Decentralized game-theoretical approaches for behaviorally-stable and efficient vehicle platooning

Published in Transportation Research Part B: Methodological, 2021

This paper proposes a decentralized game-theoretical approach for vehicle platooning.

Recommended citation: Sun, X., & Yin, Y*. (2021). "Decentralized game-theoretical approaches for behaviorally-stable and efficient vehicle platooning." Transportation Research Part B: Methodological, 153, 45-69. [TR-Part B][PDF(pre-print)]
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Integrated Planning of Static and Dynamic Charging Infrastructure to Support Electric Vehicles for Inter-city Trips

Published in Transportation Research Part D: Transport and Environment, 2020

This paper discusses integrated planning of static and dynamic charging infrastructure for electric vehicles.

Recommended citation: Sun, X., Chen, Z., and Yin, Y*., (2020). "Integrated Planning of Static and Dynamic Charging Infrastructure to Support Electric Vehicles for Inter-city Trips." Transportation Research Part D: Transport and Environment, 83, 102331.
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Methods for the design of safety service patrol beats: the Florida Road Ranger case study

Published in Transportation Research Record, 2018

This paper discusses methods for designing safety service patrol beats in Florida.

Recommended citation: Sun, X., Shahabi, M., Carrick, G., Yin, Y*., Srinivasan, S., & Shirmohammadi, N. (2018). "Methods for the design of safety service patrol beats: the Florida Road Ranger case study." Transportation Research Record, 2672(14), 50-60.
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