Passing operations on a recreational two-lane, two-way highway

A study was conducted of passing maneuvers in selected passing zones over a 21-mi segment of a principal arterial, two-lane, two-way roadway in northern Wisconsin. Within the project, passing was restricted to 33% of the roadway length due to horizontal and vertical geometrics. Five independent sites were monitored using both field observers and directional speed and volume recorders. Timed video-recorders were also placed at two sites. The data were gathered on three peak summer weekends in 1988. Operational data, segregated into 15-min intervals, included information on directional flows, average speeds, and passing operations. The data conformed with AASHTO expectations and indicated that on recreational weekends with traffic volumes of 200 to 250 veh/hr in the major direction and 85 to 175 veh/hr in the minor direction, 25 to 35% of all passes were made in the presence of an opposing vehicle, an average of 21 passes per hour were completed with duration of time in the opposing lane (at 60 mph) of 12.2 sec, and pass aborts comprised 0.8% of all passes. Under higher flow levels of 330 to 420 veh/hr in the major direction and 70 to 170 veh/hr in the minor direction, 26 to 50% of all passes were made in the presence of an opposing vehicle, an average of 16 passes per hour were completed with duration of time in the opposing lane of 11.3 sec, and pass aborts comprised up to 7% of all passes where passing was restricted to 33% for a 10- to 15-mi segment. The data indicate that (a) the passing driver's decision threshold is negatively affected by the inability to pass, (b) this effect increases significantly at volume levels as low as 500 veh/hr two-way, and (c) passing drivers may be significantly overestimating their ability to complete passing maneuvers safely.