A Benefit-Cost Analysis Tool for Assessing Guardrail Needs for Two-Lane Rural Roads in Virginia

About the report:

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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