Left-Turn and In-Lane Rumbel Strip Treatments for Rural Intersections

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Left-Turn and In-Lane Rumbel Strip Treatments for Rural Intersections

K. Fitzpatrick / M. A. Brewer / A. H. Parham

Studies were conducted on left-turn behavior, left-turn lane guidelines, and in-lane rumble strips. Behavior on the major road at a T-intersection is influenced by the width and type of the shoulder. When a wide-level of shoulder was provided, a large percentage of the drivers, up to 95 percent, drove on the shoulder at speeds near the operating speed of the roadway. At the site where the shoulder was retrofitted using available materials and widened from 3 ft (0.9 m) to 10 ft (3.1 m) just prior to the intersection, only 19 to 29 percent of the drivers used the shoulder. The Harmelink model is a widely accepted approach for determining whether to consider a left-turn lane and is the basis for the criteria included in the American Association of State Highway Transportation Officials (AASHTO) Green Book and the Texas Department of Transportation (TxDOT) Roadway Design Manual. Findings from current research suggest that Harmelink guidelines should be modified and these findings were used to revise the criteria. In order to gauge the effectiveness of in-lane rumble strips on driver speeds, rumble strips were installed on 14 approaches to rural intersections. An analysis of the speed data revealed a small and statistically significant decrease, generally 1 to 2 mph (1.6 to 3.2 km/h) in mean and 85th percentile speeds on the approaches. An additional objective for this project was to develop informational materials on rural intersection safety.