Design Guidelines for Passing Lanes on Two-Lane Roadways (Super 2)

Wooldridge, Mark D.; Messer, Carroll J.; Heard, Barry D.; Raghupathy, Selvam; Parham, Angelia H.; Brewer, Marcus A.; Lee, Sangsoon · 2001 · ROSA P / Texas Transportation Institute. Texas A&M University

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Summary

This study addresses the need for reliable design guidelines for "Super 2" roadways, a Texas-specific design featuring periodic, short-term passing lanes on two-lane rural highways. As traffic volumes increase on existing two-lane roads, traditional four-lane expansions are often fiscally unfeasible. Super 2 designs offer a cost-effective alternative to improve traffic operations, break up platoons, and enhance safety. The research was motivated by uncertainties regarding three critical design parameters: optimum passing lane length and spacing, shoulder width requirements, and effective signing and pavement marking strategies. The objective was to develop defensible criteria suitable for inclusion in the Texas Department of Transportation (TxDOT) Roadway Design Manual. The methodology combined field data collection, microscopic simulation, and driver surveys. Researchers conducted site visits and data collection at existing Super 2 sites in Kansas and Minnesota, utilizing traffic counters and manual observation to record vehicle speeds, headways, axle counts, and passing maneuvers over six-hour periods. Data reduction involved analyzing platoon formations and vehicle behavior. Additionally, microscopic simulations were performed on a hypothetical rural highway to evaluate operational performance under varying traffic mixes and passing lane configurations. To assess driver perception, laptop-based surveys were administered to 134 Texas drivers at license renewal offices. These surveys utilized video clips and photographs to evaluate driver comprehension of specific signs, pavement markings, and geometric features, including lane choice preferences and reactions to advance warning signage. Key findings from the driver surveys revealed distinct preferences and behaviors. Seventy-one percent of respondents identified "Left Lane for Passing Only" as the clearest sign for maintaining the inside lane for passing, compared to "Keep Right Except to Pass." When presented with advance notice of a passing lane, 61 percent of drivers indicated they would wait to pass rather than attempting a maneuver sooner. Regarding pavement markings, 96 percent of drivers chose to pass using the left lane at a typical entrance, whereas only 68 percent did so when a broken marking pattern separated the lanes, with 30 percent choosing to follow the slower vehicle in the right lane. In uncongested conditions, 87–92 percent of surveyed drivers preferred the right lane, though field studies noted higher usage of the left lane in practice. The simulation and field data provided specific metrics on how lane length, spacing, and shoulder widths impact traffic flow and safety. The significance of this research lies in its provision of evidence-based design recommendations for TxDOT. By integrating operational data with driver behavioral insights, the study offers specific guidelines for signing, marking, and geometric design that optimize the effectiveness of Super 2 roadways. These guidelines aim to maximize the benefits of passing lanes—such as reduced delays and improved safety—while ensuring that design elements are intuitive and effective for motorists. The findings support the continued use of Super 2 designs as a viable, lower-cost improvement for rural two-lane highways, providing a structured approach to their implementation.

Key finding

The study produced specific design criteria for Super 2 roadways, including guidelines for passing lane length and spacing, shoulder widths, and signing strategies, derived from site evaluations, simulation, and driver surveys.

Methodology

mixed_methods

Sample size: 134

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• perceptual countermeasures
• signage environment