AI Center Seminar - AI Fundamentals series - Prof. Liu Zhiyuan

The talk is jointly organized by the EPFL AI Center and the EPFL Urban Transport Systems Laboratory (LUTS) as part of the AI Fundamentals seminar series.

Host: Prof. Nikolaos Geroliminis 

Title 
TRIP: A Progressive Traffic Reasoning Foundation Model Based on Dual Modeling of Physical and Semantic Spaces

Abstract
While large language models (LLMs) are transforming society, their reliance on next-token prediction limits their adherence to the physical constraints of transportation systems. Addressing this from an interdisciplinary perspective, this presentation identifies three core challenges in applying LLMs to transportation: information density, physical constraint satisfaction, and the disconnection between semantic reasoning and traffic physics. We propose TRIP (Transport Reasoning with Intelligence Progression), a unified framework for complex traffic tasks. First, we introduce an information-theoretic "information density" metric to develop a divide-and-conquer architecture that integrates LLMs with domain-specific traffic models. Second, to align semantic reasoning with physical laws, we propose a "progressive reasoning" paradigm where a physics-embedded simulator verifies thought nodes. To manage the exponential growth of the thought tree under limited computational budgets, we formulate the generation and verification process as a Partially Observable Markov Decision Process (POMDP) and develop an efficient dynamic-programming-based tree search algorithm. Experimental results demonstrate that this method outperforms conventional reasoning paradigms in tasks such as intersection channelization and signal timing. Finally, we present the deployment and engineering optimization of TRIP in real-world scenarios.

Bio
Prof. Liu Zhiyuan is currently the Chair Professor of Southeast University (SEU) and has been awarded the former National Science Fund for Distinguished Young Scholars. He graduated from Southeast University with a bachelor's degree in traffic engineering, and a Ph.D. from the Department of Civil Engineering of NUS. He worked as an assistant professor in the Department of Civil Engineering at Monash University, Australia. In 2015, he returned full-time to the School of Transportation of Southeast University as a professor. From May 2019 to July 2023, he served as Vice Dean, School of Transportation, and from July 2023 to March 2025, he served as Acting Dean, Graduate College of Elite Engineers, and is currently Secretary, School of Statistics and Data Science. As the first or corresponding author, he has published more than 200 papers in SCI/SSCI journals such as Nature Sustainability, Transportation Science, TR Part B/C/E, IEEE TKDE, etc. Prof. Liu currently serves as the Managing Editor of Multimodal Transportation, an international journal published by Elsevier, Area Editors of TR Part C and Associate Editors of TR Part E.