A generalized time headway model for single-lane traffic flow on two-lane, two-way roadways is developed. This model, referred to as the hyper Lang probability distribution, is a linear combination of a translated exponential function and a translated Erlang function that describe free and constrained headways, respectively. The model is general in that the negative exponential, the Erlang and the hyper-exponential functions are all special cases. The parameters of the hyper Lang headway model were evaluated for two sets of data. For the conditions under which these data were collected, the model proved to be a very sound descriptor of headways. However, it should be evaluated and substantiated for a wide range of traffic and roadway conditions.
Abstract