Rethinking the Driver Population Factor: An Examination of Interstate 80 in California

摘要

Freeway analysis procedures in the widely used Highway Capacity Manual (HCM) include theinput of a driver population factor, known as F_p, which allows the analyst to adjust the demanddepending on the familiarity of the drivers on the roadway. This is based upon the assumptionthat unfamiliar drivers will drive at slower speeds with longer headways which would requirehigher capacity. However, there has been little research supporting the use of the F_p factor, andthe HCM cautions against its use unless the analyst is fairly certain the traffic stream is actuallyunfamiliar. As an experiment, two bottlenecks in California were selected and were analyzedboth during the weekday peak and Sunday afternoons in periods where the traffic stream waslikely to be non-local. Results showed that changes in queue discharge flow were minor at thesetwo locations. Further research with additional sites and an increased awareness of the definitionof familiarity will be required confirm results from this research.