Graph neural networks (GNNs) have been extensively used in a wide variety of domains in recent years. Owing to their power in analyzing graph-structured data, they have become broadly popular in intelligent transportation systems (ITS) applications as well. Despite their widespread applications in different transportation domains, there is no comprehensive review of recent advancements and future research directions that covers all transportation areas. Accordingly, in this survey, for the first time, we provide an overview of GNN studies in the general domain of ITS. Unlike previous surveys, which have been limited to traffic forecasting problems, we explore how GNN frameworks have evolved for different ITS applications, including traffic forecasting, demand prediction, autonomous vehicles, intersection management, parking management, urban planning, and transportation safety. Also, we micro-categorize the studies based on their transportation application to identify domain-specific research directions, opportunities, and challenges, which have been missing in previous surveys. Moreover, we identify unique and undiscussed research opportunities and directions, which is the result of reviewing a wide range of transportation applications. The neglected role of edge and graph learning in ITS applications, developing multi-modal models, and exploiting the power of unsupervised and reinforcement learning methods for developing more powerful GNNs are some examples of such new discussions in this survey. Finally, we have identified popular baseline models and datasets in each transportation domain, which facilitate the development and evaluation of future GNN-based frameworks.

Intersections are critical bottlenecks within urban transportation networks. Current models for simulating two-dimensional (2D) vehicular movements at intersections are met with limitations in accurately representing complex interactions and capturing vehicle dynamics. Accordingly, this paper proposes a novel microsimulation framework for trajectory planning and vehicular control at intersections. The model considers vehicle dynamics and control variables, such as acceleration and steering angle, and releases the popular assumption that there is full knowledge sharing or cooperation among vehicles at intersections. These features make the proposed framework more realistic compared to previous microsimulation attempts and applicable to traffic flow and environmental impact assessment studies. In addition, it efficiently operates in realtime for multiple vehicles, overcoming the limitations of offline methods. Moreover, the model is capable of accounting for driver/vehicle detection range, reaction time, and perception and prediction inaccuracies, which enhances its suitability for safety assessments. The evaluation in several scenarios indicates the ability of the proposed framework in realtime planning and following realistic and consistent 2D paths while avoiding collisions with other vehicles.