Modelling speed–density relationship in traffic streams Available to Purchase

This study set out to estimate the mean speed of passenger cars based on traffic density in two traffic conditions in Tehran, Iran: a homogeneous flow regime in urban highways and a heterogeneous flow regime in suburban highways. Three established models – Greenshields, Greenberg and Underwood – were initially used. However, for higher model compatibility and better mean speed prediction, two new models were proposed. Step-wise regression was used as the statistical analysis for all models and model evaluation was made through multi-collinearity checks, Durbin–Watson tests and coefficients of determination. Results showed poor compatibility of the three established models in a heterogeneous stream and partial compatibility in a homogeneous stream. Using developments of the established models in heterogeneous flow and a new dual-regime model in homogeneous flow, the mean speed could be predicted with higher accuracy and better compatibility.