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Open Access Publications from the University of California

Freeway Performance Measurement System (PeMS), Version 3 Phase II


This continuing PeMS project had four tasks: 1. Quantify the reduction in delay from optimum freeway operations; 2. Release travel time estimates to the public; 3. Training Caltrans staff in the use of PeMS; 4. Improve system robustness/maintenance. For task 1, we developed and implemented an algorithm that quantifes potential travel time reduction. The algorithm takes historical travel demand data from PeMS. It simulates the resulting traffic flow, based on an idealized ramp-metering algorithm, and calculates the resulting travel times on the freeway and waiting time at the ramps. As an example, the algorithm estimates that the annual congestion delay of 75 million vehiclehours in Los Angeles, District 7, could be reduced to 25 million vehicle-hours. For task 2, we developed an algorithm for travel time predictions for Los Angeles, and made it available on the PeMS website. Users could select any two points on the freeway network, and state a departure (or desired arrival) time. The algorithm finds the 15 shortest alternative travel routes and estimates a travel time for each. The user could select any of these routes. For task 3, we assisted Booz Allen & Hamilton in the preparation and presentation of PeMS training material. One training session was held in District 7. The feedback received from the participants was incorporated in PeMS v. 4. Berkeley Transportation Systems accomplished task 4 under a subcontract to U.C. Berkeley. The result was a clearly defined maintenance procedure and a very stable system.

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