Nowadays, traffic congestion becomes a big concern in many metropolitan world-widely. Traffic congestion causes numerous detrimental impacts, such as prolonged travel time, air pollution and emissions of green gas. Therefore, it is important to solve this issue so that reliability in road maintenance can be accomplished. However, the mechanism of evolution of traffic congestion in an urban area is somehow unclear. This is crucial to traffic operates and participants since the congestion pattern can reveal the keys to alleviate the negative impacts on the society and environment. The main objective of the study is to explore the congestion patterns in an urban context with the help of trajectory dataset from a first-of-its-kind experiment pNEUMA. This field experiment provided a high-resolution GPS traces data which contains all vehicles attributes including type of vehicle, location, speed associated with timestamps and etc., in the populated zone of Athens City, Greece. The study adopts a series of methods to fulfill the goal. Firstly, the trajectory data is processed to discard the static records and prepared for map-matching. Next, a Hidden Markov Method algorithm is employed to link the traces of vehicles to the road network. Inspired by the concept of virtual detector loops, the traffic characteristics on every travelled link will be calculated and analyzed. The time series method will be applied to find out the temporal trend of traffic streams. Finally, a proposed algorithm will distinguish the traffic states and define the congestion on every detector. The result reveals the spatio-temporal distribution of traffic congestion in Athens during 8:00 to 9:30. Focusing on the representing street, the conclusions are: traffic congestion intend to form at the merging sections of a primary and secondary roads. And traffic congestion propagates along the traffic travel direction in the very beginning. The longest duration of congestion state on the research corridor reached up to ten minutes.     «

Nowadays, traffic congestion becomes a big concern in many metropolitan world-widely. Traffic congestion causes numerous detrimental impacts, such as prolonged travel time, air pollution and emissions of green gas. Therefore, it is important to solve this issue so that reliability in road maintenance can be accomplished. However, the mechanism of evolution of traffic congestion in an urban area is somehow unclear. This is crucial to traffic operates and participants since the congestion pattern...     »