CAR-FOLLOWING HEADWAYS ON FREEWAYS INTERPRETED BY THE SEMI-POISSON HEADWAY DISTRIBUTION MODEL.

The study described was conducted to investigate driver car-following patterns on freeways, particularly as a function of traffic flow level, using a headway distribution model. The ″semi-Poisson″ model proposed by D. J. Buckley, is applied to a data base consisting of 42,000 observed headways from a single lane of an urban freeway over a range of flow from 900 to 2000 vehicles per lane per hour. A previously developed computational method allows the distribution of followers headways to be calculated directly from the observed total headway distribution by numerically solving an integral equation without introducing a parametric form for the followers distribution.