Time headway distribution model and relationships between its parameters and traffic volume

Headway distribution is one of the basic characteristics of traffic flow. The objects of this paper is to analyze the headway characteristics of the no-passing rural two-lane roads, and to obtain the reasonable theoretical headway distribution models. The lognormal distribution was used for followers' headway distributions and the negative exponential distribution for leaders'. Their parameters and proportion of the foilowers in the total traffic were estimated and analyzed the relationships between these estimated values and traffic volume. We obtained the results that parameters of the followers' headway distribution (lognormal distribution) was almost unchanged for traffic volume, and that the relationships between parameter of leaders distribution (exponential distribution) and traffic volume was essentially straight line, and that the proportion of followers in the total traffic. increased according to some curve line as traffic volume increased.