Significance of Fundamental Diagrams to First-Order Macroscopic Traffic Modelling

Abstract

Macroscopic models are computationally effective and generate reliable estimates of traffic dynamics based upon the principles of flow conservation and propagation, in which the underlying fundamental diagram (i.e. flow-density relationship) has an important part in capturing the plausible traffic propagation over time and space. This study investigates in practice whether, and in what extent, the calibration of the fundamental diagram affects the performance of macroscopic traffic modelling by using motorway data. For study purposes, a modified version of the first-order Cell Transmission Model (CTM) is adopted in order to allow the use of different fundamental diagrams instead of the traditional triangular one. Traffic data from the MIDAS (Motorway Incident Detection and Automatic Signalling) dataset for M25 motorway in the UK are used for the case studies. The findings of this study demonstrate the significance of selecting the best-suited fundamental diagram to each traffic scenario in order to improve the accuracy of traffic modelling and contribute to the performance analysis and management of motorways.