Accuracy of Networkwide Traffic States Estimated from Mobile Probe Data

Reproducible relationships between networkwide averages of local traffic metrics can be used to describe network dynamics and to inform large-scale strategies for traffic control. Even though relationships such as the network fundamental diagram or macroscopic fundamental diagram (MFD), which relates average vehicle flow and density, have been verified with empirical data, these relationships remain notoriously difficult to estimate in practice. Data from mobile probe vehicles are proposed for use in estimating the relevant networkwide traffic metrics, which include the average flow, density, speed, accumulation, and exit flow of vehicles. The method has low data requirements: only the distances traveled by probes at various times and the probe and nonprobe vehicle counts at fixed locations. This information is becoming increasingly available because of advances in intelligent transportation systems, GPS, and mobile computing. Probe and nonprobe vehicle counts at fixed locations can be estimated by combining probe vehicle data with data from fixed detectors. The uncertainty of these measurements also can be estimated from probe vehicle data. This information then can be used to estimate the MFD and other networkwide relationships directly or to monitor traffic in real time. This method was tested on a microsimulated network and was accurate when mobile probe penetration rates reached about 20%.