United States Department of Transportation
i
Examine Trade-Offs Between Center Separation and Shoulder Width Allotment for a Given Roadway Width
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2021-11-01
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[PDF-3.42 MB]
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Edition:August 2019–July 2021
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Abstract:In Texas, four-lane undivided roadways constitute a significant amount of mileage in rural areas. These highways have poor safety performance compared to other cross sections. However, there is not always sufficient space within the available right of way to accommodate a traditional four-lane divided cross section. Thus, a framework can assist road design engineers in making decisions on cross sections for new and resurfaced rural roadway segments to optimize operational and safety performance. In this research project, researchers evaluated the safety and operational benefits of converting four-lane undivided highways into other cross-section alternatives without changing the total roadway width. First, researchers selected a sample of rural highway segments with various cross sections, including four-lane undivided, four lane with 4-ft median buffer, four lane with two-way left-turn lane (TWLTL), Super 2, and Super 2 with TWLTL. They analyzed crash data on each cross section to determine the relationship between crash frequency, exposure, access-point density, horizontal curvature, cross-sectional widths, and operating speed variables. Second, researchers collected operating speed data in the field and developed VISSIM simulation models to evaluate the operational impacts of different cross sections considered in the project. Based on safety and operational effects, researchers developed a framework that allows the analyst to select a cross section depending on traffic volume, heavy vehicle mix, cross-sectional width, and access-point density.
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