Professor Nie's research covers various aspects of transportation systems analysis, ranging from developing specialized routing algorithms to designing Pareto-improving congestion pricing schemes. Despite their diversity, most problems that he has been working on address research questions that not only are of theoretical interest but also promise relevant real-world impacts.

Prof. Nie's primary interest is to better understand and predict the behavior of transportation networks, and to formulate new design and control strategies to improve mobility, reliability and sustainability of these systems. Unlike other networks such as communication and social networks, the behavior of a transportation network depends on the interactions between human activities (travel choice and driving behavior), physical characteristics of the infrastructure and network topology. As a result, his analyses of transportation systems take an interdisciplinary approach that draws on tools from optimization, network science, traffic flow theory, economics, and statistics.