Scientific paper ID 1221 : 2015/3

Traffic flow theory establishes two basic terms to define traffic flow speed: space mean speed and time mean speed. Research on how speed in free traffic flow depends on the size of longitudinal gradient is related to the need for determining travel time and operating costs of road users. According to HCM manuals, flow speed has been deprived from its primary role in defining level of service, while domestic recommendations give flow speed the role of primary indicator. Subject matter of this paper is the analysis of free traffic flow speed dependence on different factors, primarily weather conditions. The goal is to formulate deterministic models which optimally describe free flow speed on two-lane roads.