Rethinking the Driver Population Factor

Abstract

Freeway analysis procedures in the widely used Highway Capacity Manual (HCM) include the input of a driver population factor (F_p), which allows the analyst to adjust the demand depending on the familiarity of drivers with the roadway. This adjustment is based on the assumption that unfamiliar drivers will drive at slower speeds with longer headways and that higher capacity would therefore be required. However, little research supports the use of the F_p, and the HCM cautions against the use of F_p unless the analyst is fairly certain the traffic stream is actually unfamiliar with the roadway. As an experiment, three bottlenecks in California were selected and analyzed during the weekday peaks and weekend afternoons in periods during which the traffic stream was likely to be nonlocal. The results showed that the changes in flow were minor at all three locations. Further research with additional sites and an increased awareness of the definition of familiarity will be required to confirm the results from this research.

Get full access to this article

View all access options for this article.

References

Highway Capacity Manual 2010. Transportation Research Board of the National Academies, Washington, D.C., 2010.

California Performance Measurement System (PeMS). http://pems.dot.ca.gov. Accessed July 1, 2012.

Special Report 209: Highway Capacity Manual. TRB, National Research Council, Washington, D.C., 1985.

Highway Capacity Manual. TRB, National Research Council, Washington, D.C., 2000.

, Huang

, and Mierzejewski

Driver Population Factors in Freeway Capacity. Center for Urban Transportation Research, University of South Florida, Tampa, 1997.

Sharma

Driver Population Factor in New Highway Capacity Manual. Journal of Transportation Engineering, Vol. 113, No. 5, 1987, pp. 575–579.

Brilon

, and Ponzlet

Variability of Speed–Flow Relationships on German Autobahns. In Transportation Research Record 1555, TRB, National Research Council, Washington, D.C., 1996, pp. 91–98.

Zhou

, Lu

J. J.

, Mierzejewski

E. A.

, and Le

Development of Driver Population Factors for Capacity Analysis of Signalized Intersections. In Transportation Research Record: Journal of the Transportation Research Board, No. 1710, TRB, National Research Council, Washington, D.C., 2000, pp. 239–245.

Heaslip

, Louisell

, and Collura

Driver Population Adjustment Factors for Highway Capacity Manual‘s Work Zone Capacity Equation. Presented at 87th Annual Meeting of the Transportation Research Board, Washington, D.C., 2008.