Car-Following Interaction and the Definition of Free-Moving Vehicles on Two-Lane Rural Highways

Abstract

This paper presents an investigation into car-following interactions on two-lane rural highways. Empirical data from several study sites on two-lane and four-lane rural highways in the state of Montana were used in this investigation. Three separate yet relevant analyses are presented in this paper. The first analysis involves a preliminary characterization of time headways and their distributions and shows how they are affected by passing restrictions on two-lane highways. The second analysis presented in this paper involves an investigation of speed-headway relationship to establish a headway threshold that could be used in defining free-moving vehicles on two-lane highways. The third and last analysis investigates the “following by choice” phenomenon on two-lane highways using data from two-lane as well as four-lane study sites. The study found that the car-following interaction generally ceases when headways exceed a value of approximately six seconds. Also, a significant proportion of drivers choose to maintain relatively short headways while following other vehicles on two-lane highways regardless of passing restrictions.