Freeway Performance Measurement System: Mining Loop Detector Data

Performance Measurement System (PeMS) is a freeway performance measurement system for all of California. It processes 2 GB/day of 30-s loop detector data in real time to produce useful information. At any time managers can have a uniform, comprehensive assessment of freeway performance. Traffic engineers can base their operational decisions on knowledge of the current status of the freeway network. Planners can determine whether congestion bottlenecks can be alleviated by improving operations or by minor capital improvements. Travelers can obtain the current shortest route and travel time estimates. Researchers can validate their theory and calibrate simulation models. PeMS, which has been in stable operation for 18 months, is a low-cost system. It uses the California Department of Transportation (Caltrans) network for data acquisition and is easy to deploy and maintain. It takes under 6 weeks to bring a Caltrans district online, and functionality can be added incrementally. PeMS applications are accessed over the World Wide Web; custom applications can work directly with the PeMS database. Built as a prototype, PeMS can be transitioned into a 7 × 24 production system. The PeMS architecture and use are described.