Determining Free-Flow Speed on Different Classes of Rural Two-Lane Highways

Current analytical free-flow speed models consider all rural two-lane highways as the same road type despite their different functional significance in network. The aim of this paper is to develop a prediction model for function limit and geometric characteristics classes highways. research was conducted on 50 representative sections two equipped with automatic traffic counters Serbia. In order appropriate models, it necessary determine threshold values vehicle time headway both highways, based total number 191,720 vehicles. obtained results show that there are differences classes. Namely, determined Class I amounted 6.3 s, II 8.4 s. showed had highest impact followed by horizontal curve radius shoulder width.