Integration of a cell transmission model and macroscopic fundamental diagram: Network aggregation for dynamic traffic models

Network size can have a significant impact on the computational performance of traffic simulation models. Due to this, methods to reduce network size can be valuable when analyzing large networks. In this research, a novel model integrating a Cell Transmission Model (CTM) with the Macroscopic Fundamental Diagram (MFD) for urban networks is proposed and its effects analyzed. The concept that underlies this work is that a road network can be classified into two types of networks: the first includes roads that are modeled using CTM, and the second are components of the network that can be aggregated into large self-contained cells that also maintain properties of the MFD. To test the proposed model and its computational efficiency, a case study involving an evacuation is introduced. The network and its demand, built from the Southeast Louisiana Hurricane Katrina evacuation event, were modeled using a combination of CTM and MFD. The spatio-temporal profiles of volume and speeds on key routes and destinations from the proposed model were compared to observed data from the event. The results suggest that the model was able to realistically capture the observed shock wave phenomena, and reproduce the spatio-temporal characteristics of the evacuation traffic. This simple methodology has considerable potential to improve computational efficiency in dynamic traffic assignment models, particularly for those large-scale networks and processes, while ensuring that the traffic dynamics are realistically modeled.