PeMS is a freeway performance measurement system for all of California. It processes 2 GB/day of 30-second loop detector data in real time to produce useful information. Managers at any time can have a uniform, and comprehensive assessment of freeway performance. Traffic engineers can base their operational decisions on knowledge of the current state 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 is a low-cost system. It uses the Caltrans network for data acquisition. It is easy to deploy and maintain. It takes under six weeks to bring a Caltrans district online. Functionality can be added incrementally. PeMS applications are accessed over the World Wide Web. Custom applications can work directly with the PeMS database. PeMS has been in stable operation for 18 months. Built as a prototype, PeMS can be transitioned into a 7x24 production system. The paper describes the PeMS architecture and use.
The paper describes a methodology and its application to measure total, recurrent, and nonrecurrent (incident related) delay on urban freeways. The methodology uses data from loop detectors and calculates the average and the probability distribution of delays. Application of the methodology to two real-life freeway corridors-one in Los Angeles and the other in the Bay Area-indicates that reliable measurement of congestion should also provide measures of uncertainty in congestion. In the two applications, incident-related delay is found to be between 13 to 30 percent of the total congestion delay during peak periods. The methodology also quantifies the congestion impacts on travel time and travel time variability.
The I-880 field experiment has produced one of the largest data bases on incidents and freeway traffic-flow characteristics ever compiled. Field data on incidents were collected through observations of probe-vehicle drivers before and after the implementation of freeway service patrols (FSPs) over a freeway section. Supplementary information was collected from the California Highway Patrol’s computer-aided dispatch system, FSPs, and tow-truck company logs. The incident patterns are described and the major factors affecting incident frequency and duration are identified. FSPs significantly reduced the response times but did not have a significant effect on the duration of all incidents.
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