United States Department of Transportation
i
Procedures for Setting Advisory Speeds on Curves
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2011-06-01
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[PDF-2.53 MB]
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Abstract:Horizontal curves are a necessary component of the highway alignment; however, they tend to be associated with a disproportionate number of severe crashes. Warning signs are intended to improve curve safety by alerting the driver to a change in geometry that may not be apparent or expected. However, several research projects conducted in the last 20 years have consistently shown that drivers are not responding to curve warning signs or complying with the Advisory Speed plaque. It is estimated that half of all speeding related roadway departure crashes occur on curves. One of the reasons that curves are overrepresented in speeding related fatalities is due, in part, to advisory speeds that are not consistent, and therefore, not credible. A project by Texas Transportation Institute (TTI), Texas Research Project 0-5439 "Identifying and Testing Effective Advisory Speed Setting Procedures", exemplifies how current procedures for setting advisory speed on curves are not reliable, and has developed new criteria and a new procedure that are more consistent with driver expectation. The new procedure involves the use of an Excel spreadsheet and a handbook for applying the new criteria. The procedures described in the handbook are intended to improve consistency in advisory speed signing and, hopefully, driver compliance with the advisory speed. The handbook describes; 1) guidelines for determining when an advisory speed is needed; 2) criteria for identifying the appropriate advisory speed; 3) an engineering study method for determining the advisory speed; and 4) guidelines for selecting other curve related traffic control devices.
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