The purpose of this research was to determine the singular and combined effects of impedance distance, impedance speed, passing sight distance, and traffic volume on driver acceptance of passing opportunities as they occur on rural two-lane highways. A further aim was to describe empirically the effects of these variables on the nature of the passing maneuver.

The report presents a detailed discussion of the methodology, test sites, instrumentation, experimental procedures and major results. Controlled road tests were used in which the subject driver was unaware that he was involved in an experiment. An experimenter-controlled instrumented van produced and regulated the impedance conditions. Passing site distance was controlled through test site selection, and traffic volume at the test sites was treated as a sampling variable.

The major results indicate that passing sight distance is the predominant variable influencing the decision to pass. An analysis of covariance controlling for the effects of traffic volume yielded statically significant effect for impedance speed and the impedance distance/sight distance interaction.