Traffic characteristics on two-lane highway downgrades.

This paper is also published in the Proceedings of the Second International Symposium on Highway Capacity, Volume 1, p. 55-70, published by the Australian Road Research Board ARRB Ltd, 1994 and for the abstract see IRRD 861360 (below). Similar work is also published in Transportation Research 1996, Volume 30A, No. 2, p. 119-133 (see IRRD 879074). This paper presents the findings of a study of traffic flow on long downgrades on the primary highway system in Western Canada. Downgrade data was collected on three long, steep downgrades using a time lapse video camera. The findings indicated that while truck speeds on level terrain are only slightly slower than passenger cars, on downgrades the presence of trucks noticeably affects speed-flow relationships. Both the Hyperlang and Schuhl headway distributions produced excellent fits to the headway data. The data yielded over 6000 platoons. The Geometric, Borel-Tanner, and one parameter Miller distributions provided a good representation of traffic flow on downgrades only under some conditions, however, conditions, however, the two-parameter Miller distribution produced very good fits in all cases of platoon size distributions. (A)