Recent research has promoted the concept of matching highway-safety features to the type of roadway facility and its traffic conditions. According to NCHRP Report 350
, "Recommended Procedures for the Safety Evaluation of Highway-Safety Features," a safety feature may be developed to meet one of up to six test levels, depending on the type of feature. Further, a feature may be designed for temporary (work zone) or permanent applications. Under this concept, features developed for the lower test levels, which have minimal containment capabilities for heavier vehicles, may be considered applicable for low-speed, low-volume conditions. While the test levels have been defined, recommended guidelines for their application have only been developed for bridge rails. Transportation agencies (federal, state, and local) are being required to make decisions on the use of features to comply with NCHRP Report 350
without guidelines on the appropriateness of highway-safety features including permanent and temporary traffic barriers, crash cushions, terminals, truck-mounted attenuators, breakaway supports, rumble strips, and cross-sectional elements for specific conditions.
The American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide
(RDG) provides general guidelines to assist design personnel in determining when specific highway-safety features may be needed. The RDG presents these guidelines in terms of roadside terrain features, traffic volumes, design speed, accident probability, and environmental conditions. It does not, however, provide guidance on the specific type of highway-safety feature most appropriate for combinations of these conditions. Objective guidelines are needed not only to identify site conditions where a safety feature is needed but also to identify the most appropriate feature for that site. The guidelines should take into account roadway and traffic conditions, and the characteristics of candidate features (e.g., impact performance, life-cycle costs, durability, and maintainability). Inappropriate selection of a highway-safety feature at a particular site can be detrimental to the overall safety of the roadway or wasteful of scarce resources.
The objective of this research was to develop route specific guidelines for the application of guardrail and guardrail terminals. Supplemental recommendations were prepared to help designers identify when a more detailed site specific analysis should be considered.
To accomplish the project objectives, the following tasks were conducted: (1) Update crash severity and cost figures. (2) Develop representative highway characteristics including such items as shoulder width, location and degree of roadside slopes, and hazard offset. (3) Identify hazard configurations. (4) Select safety treatment alternatives. (5) Conduct a benefit/cost analysis. (6) Develop route specific guidelines. (7) Prepare example applications. (8) Develop a research plan for Phase II.
: The project has been completed and the final report published.
Product Availability: NCHRP Report 638: Guidelines for Guardrail Implementation