Probe Sampling Strategies for Traffic Monitoring Systems Based on Wireless Location Technology

Transportation agencies have become very interested in traffic monitoring systems based on wireless location technology (WLT) since they offer the potential of collecting travel time data across a wide portion of the road system. Prior tests of WLT-based systems have been unsuccessful, in part because they have treated the road network as a homogeneous entity. This “area-wide” method has inherent limitations, causing congested roadways to be over sampled and uncongested and low volume roads to be under sampled. This project developed a methodology to estimate sampling parameters based on localized traffic conditions in the network, termed a “zonal approach.” In zonal WLT systems, the roadway network is disaggregated into smaller areas, termed “zones,” based on cellular coverage areas. In this research, two zonal sampling strategies were examined and tested using three simulated networks. When the road network is complex, the zonal priority sampling strategy was found to distribute probes throughout the network and produced a larger number of speed estimates on uncongested and low volume roads. Moreover, the zonal priority strategy improved speed estimation accuracy by 10% over the other two sampling strategies. For networks with simple geometry or uniform congested traffic conditions, there were no significant differences among the sampling strategies. The results of this research indicate that the homogeneous approach used by earlier deployments has limitations, and results could be potentially improved by tailoring sampling parameters to a more localized level.