Rural Two-Lane Passing Headways and Platooning

Abstract

Field observations and video records were made at three northwest Arkansas locations where vehicles on a two-lane rural highway encountered passing/climbing lane sections. At all three sites, vehicles had traversed roadway sections with limited passing opportunities before they encountered passing sections on slight to moderate upgrades. By studying traffic at such sites, one can observe the behaviors of motorists who may have been restrained by slower traffic ahead, but who then encounter a relatively unconstrained environment that allows them to pass if they have been displeased or frustrated with any constraint. It was concluded from the data that at higher traffic volumes (450 vehicles per hour or higher in one direction), the arrival rate of vehicles in the samples taken probably did not follow a Poisson distribution. A simple linear regression equation was developed to express the proportion of vehicles in platoons as a function of the total one-direction traffic volume. Two of the sites had shorter passing lanes, whereas the passing lane at the third site was almost twice as long as those at the other two sites. Passing success declined when headways were greater than 2.0 sec. At both the short-passing-lane and the long-passing-lane sites, when headways were 3.0 sec or more and platoon speeds were 80 kph (50 mph) or more, 85 percent of drivers did not exhibit a desire to pass. This suggests that many drivers find a low level of congestion or platooning on two-lane rural roads to be tolerable.