Daytime High-Speed Passing Maneuvers Observed on Rural Two-Lane, Two-Way Highway

Abstract

Daytime high-speed passing maneuvers were recorded along a straight and flat 15-mi section of a rural two-lane, two-way highway in Texas. The posted speed limit was 70 mph. Passing maneuvers were covertly recorded from the overtaken vehicle, which was driven at three specific study speeds: 55, 60, and 65 mph. A total of 105 single-vehicle daytime passes were analyzed. Speed profiles of the passing vehicles’ passes were developed for each of the three studied speeds. The results were compared with AASHTO's assumptions and criteria for minimum passing sight distance (PSD) for two-lane, two-way highways. In particular, the analysis focused on the elements associated with a passing vehicle while it occupied the opposing lane of travel. The specific elements that were studied included these four: the average passing speed, the speed differential between passing and passed vehicles, the distance traveled while making the pass, and the total elapsed time. The general findings provided support for the AASHTO PSD model. For the assumptions made, the model provided reasonable results. However, the assumptions may need to be updated or to have more flexibility added. For instance, for a 70 mph design speed, the assumed speed of the overtaken vehicle is 54 mph in the AASHTO PSD model. The PSD associated with these speeds was verified in this study. But what if the overtaken vehicle was traveling at 60 or 65 mph? The results of this study show that the current AASHTO PSD model would provide inadequate PSD values for overtaken speeds greater than those currently assumed.