DESIGN GUIDELINES FOR PASSING LANES ON TWO-LANE ROADWAYS (SUPER 2)

The use of periodic, short-term passing lanes is known in Texas as a "Super 2" design. The passing lanes may be alternating or side-by-side, but they are placed at regular intervals. Passing lanes are often constructed on two-lane roadways to improve overall traffic operations by breaking up traffic platoons and by reducing delays caused by inadequate passing opportunities over substantial lengths of roadway. During the recent design of several "Super 2" projects, questions arose in three areas: 1) optimum passing lane length and spacing; 2) shoulder width requirements; and 3) optimum signing and driver information (pavement marking, etc.) strategies. The objective of this project was to develop Super 2 design criteria in a format suitable for inclusion in the Texas Department of Transportation (TxDOT) "Roadway Design Manual." Site evaluations were conducted in Texas, Kansas, and Minnesota, including before-and-after studies of driver behavior for variations in pavement markings. A hypothetical two-lane, two-way rural highway with varying length and spacing of passing lanes was simulated under a variety of traffic mixes and two-way traffic volumes. Additionally, laptop-based surveys were conducted to determine driver reaction to various passing lane spacings, wording on related signs, shoulder widths, and pavement markings entering a passing lane section. Recommendations for the TxDOT "Roadway Design Manual" were developed based upon these activities.

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