United States Department of Transportation
i
A benefit-cost analysis tool for assessing guardrail needs for two-lane rural roads in Virginia.
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2015-10-01
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Abstract:Guardrail is installed along the roadside to shield hazards such as steep slopes and bridge piers from vehicles. Although
the Virginia Department of Transportation’s Road Design Manual provides guidance for determining where to install guardrail on
new facilities, there is no consistent approach available for evaluating guardrail needs on existing roads that explicitly considers
costs and benefits.
This study developed such an approach, focusing on low volume, two-lane rural roadways in Virginia. The Roadside
Safety Analysis Program (RSAP)—developed under NCHRP Project 22-27 and currently the most sophisticated tool available for
conducting cost-effectiveness analysis of roadside safety treatment options—was used to determine expected crash frequencies,
severities, and costs for several combinations of hazard scenarios; guardrail treatment options; and relevant roadway, roadside,
and traffic characteristics. The results of the RSAP analysis were used to develop a predictive model that relates the input
variables to the output response (benefit/cost ratio). The model is implemented in a simple spreadsheet for the quick and efficient
evaluation of proposed guardrail treatment options without the need for full-blown RSAP analysis. Application of the spreadsheet
tool is demonstrated through example problems.
A comparison of the tool’s modeling results with results obtained from RSAP is presented. The comparative results
show that benefit/cost ratio estimates provided by the tool are in good agreement with those provided by RSAP. These results
indicate that the simplified tool meets the requirements to serve as a surrogate for RSAP analysis and is therefore recommended
for benefit/cost evaluations of proposed guardrail treatment options for low volume, two-lane rural roadways in Virginia.
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