Traffic Density Estimation with the Cell Transmission Model

A macroscopic traffic flow model, called the switchingmode model (SMM), has been derived from the cell transmission model (CTM) and then applied to the estimation of traffic densities at unmonitored locations along a highway. The SMM is a hybrid system that switches among different sets of linear difference equations, or modes, depending on the mainline boundary data and the congestion status of the cells in a highway section. Using standard linear systems techniques, the observability and controllability properties of the SMM modes have been determined. Both the SMM and a density-based version of the CTM have been simulated over a section of I-210 West in Southern California, using several days of loop detector data collected during the morning rush-hour period. The simulation results show that the SMM and CTM produce density estimates that are both similar to one another and in good agreement with measured densities on I-210. The mean percentage error averaged over all the test days was approximately 13% for both models.