Influence of Various Restrictions on Speed–Flow Models

This paper presents traffic speed models developed on the basis of numerous measurements. In studies of the speed–flow relationships the following research issues were analyzed: impacts of the speed limit, traffic flow, traffic flow composition, and time of day on speed–flow and impacts of qualitative road and roadside features (cross sections, road function, accessibility, intensity of development, roadside pedestrian traffic) on free-flow speed. The research included road sections with numerous constraints of traffic freedom. Such sections include sections of roads through built-up areas (small communities and towns). Regression analysis using generalized multiple regression was the basic tool in investigations. In addition, in analyzing data from speed measurements, the classic form of the logit function for a multiple-valued regression was applied. The analyses showed that even at general and posted speed limits the characteristic traffic flow–speed relations can be identified. The shape of these relations is characteristic of empirical results in which the spread of recorded values is typical for randomness and impacts of local factors. Average speed in traffic flow depends not only on geometric alignment of a road cross section but also on local factors and speed limits. Speed in free-flow traffic is significantly influenced by qualitative road and roadside characteristics. Most important of these factors are type of cross section, intensity of roadside development, and accessibility of the road.