BEYOND THE BPR CURVE: UPDATING SPEED-FLOW AND SPEED-CAPACITY RELATIONSHIPS IN TRAFFIC ASSIGNMENT

This paper, which appears in a compendium of conference papers, describes a research effort focused on refining the planning model, and specifically, modifying the speed-flow curves in traffic assignment based on heuristic investigations and literature review. Researchers used a speed-flow curve similar to the one recommended in the "revised" Highway Capacity Manual. The challenge was to derive a speed-flow relationship that gave realistic speeds for demands exceeding capacities. Researchers also developed a "facility type-area type" classification system for all links in the region to estimate their capacities as accurately as possible. Results were validated with field data for 41 percent of the total 2,156 freeway kilometers (1,340 miles) in the highway network for the San Francisco Bay Area.