United States Department of Transportation
i
Effective Superelevation for Large Trucks on Sharp Curves and Steep Grades
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2002-10-01
[PDF-4.28 MB]
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Edition:Final Report
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Design;NTL-SAFETY AND SECURITY-Accidents;NTL-SAFETY AND SECURITY-Highway Safety;
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Abstract:This project was undertaken to identify the particular problems faced by trucks on sharp curves on steep grades, such as rebuilt switchback curves on mountainous two-lane, two-way roads and the high speed downgrade curves found on West Virginia's limited access roadways, to determine appropriate superevelation rates for trucks under these circumstances. A review of the engineering literature relative to the influence of roadway design and truck characteristics on vehicle handling and stability indicated that for large trucks on such geometry the margin of safety is small.
Several analytical models (static in nature) were developed to evaluate the situation. It was concluded that on sharp curves on steep downgrades additional superevelation is indicated in the downgrade direction, while less superevelation is needed in the upgrade direction. However, this preliminary analysis left many unanswered questions. Crash data were analyzed, spot speed data collected and truck drivers interviewed in an effort to gain additional insight into the problem. Before using the models developed in this research in the geometric design of roadways, the models need to be critically reviewed and further enhanced, including inclusion of vehicle dynamics.
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