Measuring wave velocities on highways during congestion using cross spectral analysis

Previous research has shown that disturbances in the traffic state (flow, occupancy, and velocity) propagate upstream with nearly constant velocity through congested freeway traffic. The velocities of these backward propagating waves can be estimated by comparing the time series of the state observed at successive detector stations on the same congested freeway. The earlier research examined a relatively small number of disturbances using labor-intensive techniques. In order to characterize the disturbances more comprehensively, this paper develops an automated method to extract their velocity in the presence of noise. Time delay estimation (TDE), a common technique in digital signal processing, was used to solve the problem. Out of the TDE algorithms, cross-spectral analysis was chosen to analyze one month of data from the Berkeley Highway Laboratory (BHL) and the results are presented.