Guidelines for Guardrail on Low-volume Roads

About the report:

Guardrail is a type of longitudinal barrier installed along a roadside to shield vehicles from hazards. Guardrail is itself a hazard and should be installed only if it would reduce the severity of accidents. Accordingly, the American Association of State Highway and Transportation Officials (AASHTO) has guidelines that can be used to evaluate the need for guardrail. The Virginia Department of Transportation (VDOT) has, for the most part, adopted these guidelines for its interstate, primary, and arterial road systems. However, these guidelines are generally based on information concerning high-speed, high-volume roads; consequently, VDOT bases decisions regarding the need for guardrail on its secondary road system entirely on engineering judgment. Guidelines are needed to assist in evaluating the need for guardrail on secondary roads, which most typically have low-volume and low-speed traffic. The primary advantage of such guidelines is that guardrail will be more uniformly installed on low-volume roads. Final decisions regarding the use of guardrail would be dependent on sound engineering judgment; however, all decision-making would at least be based on the same methodology and analyses. Guidelines and uniform installations are of considerable benefit in deciding questions of liability. Formal guidelines should also increase the safety of the motoring public on low volume roads. Finally, they will provide for a more cost-effective use of guardrail. The purpose of this research was to develop such guidelines. The original scope of the study was to develop guidelines from existing practices as reported in the literature and from a survey of other states. However, it was concluded from that research that VDOT needed guidelines based on Virginia-specific data. Accordingly, the scope of the study was expanded to include the application of the computer program ROADSIDE, which was used to develop guidelines to determine whether guardrail is needed on fill embankments and for fixed objects on secondary roads in Virginia. The former guidelines were defined in terms of volumes and fill heights for a given slope, whereas the latter guidelines were defined in terms of a required clear zone for a given volume. It is recommended that VDOT consider adopting the guidelines developed in the report to evaluate the need for guardrail on its secondary roads.

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