The National Academies

NCHRP 22-16 [Completed]

Development of an Improved Roadside Barrier System

  Project Data
Funds: $200,00 (Phase I)
Research Agency: West Virginia University Research Corporation
Principal Investigator: Karl E. Barth
Effective Date: 7/16/1999
Completion Date: 6/30/2002

Background: Roadside barrier systems have been developed over the years to safely redirect vehicles that leave the roadway. Many different rigid, semi-rigid, and flexible designs for roadside barriers have evolved. The most common system consists of a steel W-beam rail on wood or steel posts with end treatments and transitions of various designs using similar materials. Such barrier systems are intended to be sacrificial, which requires substantial replacement after major vehicle impact. Even low-energy impacts can bend and damage the steel rails and displace posts enough that the barrier might not perform properly in a subsequent impact. Maintenance crews must spend considerable time maintaining these systems, which results in high costs and safety risks to motorists and highway workers. Concrete safety-shaped barriers of varying designs have also been used as roadside barriers. Concrete barriers, while higher in initial cost, tend to require less maintenance, but are less forgiving in severe impacts.

The need exists to design an improved, roadside barrier system that meets crashworthiness evaluation criteria and performs better relative to other factors (e.g., cost, ease of installation, maintainability) than the strong post, W-beam guardrail (i.e., G4-1 in the AASHTO Roadside Design Guide). A holistic research approach is anticipated to cover all aspects of designing, installing, and maintaining a roadside barrier system. This research is expected to (1) determine suitable materials to reduce life-cycle cost and maintenance of the barrier system; (2) develop innovative designs or design improvements; (3) apply analytic and simulation methods to effectively evaluate and refine promising designs for various applications; and (4) assess the adaptability of the barrier system to special situations (e.g., barriers installed close to the edge of steep fill slopes).

Objective: The ultimate goal of research in this area was to develop an improved roadside barrier system that will meet the latest crashworthiness criteria. The system would be expected to provide increased safety, competitive initial and life-cycle costs, reduced maintenance, and greater flexibility in field applications over a typical strong-post, W-beam guardrail (i.e., G4-1 system). The objectives of this project were to (1) investigate the feasibility of various candidate design concepts for an improved roadside barrier system, (2) develop and evaluate the most promising design concept(s), and (3) formulate plans for full development and testing of the most promising design concept(s).

This project was expected to result in a detailed design for an improved roadside barrier system that is available for unrestricted, royalty-free use by state highway agencies. This project focused on the development of an improved roadside barrier system for unidirectional impacts. The system will incorporate an end treatment, a length of need element, and a transition to a vertical concrete wall. Variations in the design to meet the specific requirements of individual highway agencies will need to be developed in other research. Modifications of the design for an improved roadside barrier system for median barrier application (i.e., bi-directional impacts) are not expected to be part of this research.

Tasks: It was envisioned that this project would be undertaken in two phases with the tasks described below.

Phase I--Design Concept Development and Feasibility Analysis: (1) Review the literature to gather information on innovative design concepts, possible materials, and issues related to the use of roadside barriers. The review should include foreign documents and patents to identify prospective new designs and material applications. (2) Contact state DOTs to determine their concerns and the major issues that affect the type and the use of barriers in their state (i.e., soil conditions, snow, life-cycle cost, maintainability, reusability, slope break adaptability, crashworthiness, and aesthetics). The project panel will review the questions prior to distribution to the DOTs. (3) Establish basic functional requirements for an improved roadside barrier system from the information gathered in Tasks 1 and 2. The basic requirements should apply to all elements of a roadside barrier system across a full range of applications (e.g., different side slopes, varying climates). These functional requirements are expected to provide the basis for conceptualizing an improved roadside barrier system and to provide a framework for comparison of alternative design concepts. The degree to which a typical strong-post, W-beam rail system meets these functional requirements shall be determined as a benchmark for assessment of the various innovative design concepts to be developed in Task 4. The NCHRP panel expects to review the functional requirements and rationale for them within 6 months of the start of the contract. (4) Develop preliminary design concepts for at least three improved roadside barrier systems. A systematic process for integrating new design concepts and materials for an improved roadside barrier system should be followed. Cite the extent of use that can be expected with each of the improved design concepts. (5) Conduct preliminary analyses of the conceptual designs for an improved roadside barrier system using analytical models, physical tests, and simple simulations, as appropriate. Compare alternative conceptual designs with the strong-post W-beam system for the functional requirements established in Task 3. (6) Prepare an interim report documenting the findings of Phase I. The report shall provide detailed descriptions of the preliminary design concepts for review by the panel and the AASHTO Task Force on Roadside Safety. The interim report shall also outline the process(es) that will be used to develop the detailed designs in Phase II. Meet with the panel to review and select the most appropriate design concept(s) for development in Phase II of the project. The potential impacts of an improved design concept will be considered in selecting the concept(s) that will be developed in Phase II.

Phase II--Detailed Design Development: (7) Develop the preliminary designs for the concept(s) selected in Task 6. Prepare detailed working drawings and appropriate analyses, such as static and dynamic physical tests, simulations, and other efforts to validate the designs. (8) Estimate the costs and benefits associated with the detailed design(s) for selected site conditions. The costs and benefits are expected to include initial, maintenance, and life-cycle costs as well as safety cost-effectiveness. (9) Formulate a plan and cost estimate to complete the required full-scale crash testing of the detailed design(s). (10) Present the detailed design(s) to two AASHTO committees (e.g., Task Force on Roadside Safety, Standing Committee on Highway Traffic Safety) designated by the NCHRP panel to solicit feedback. The panel will direct the Contractor to revise the design(s) based on feedback. (11) Prepare a final report documenting the efforts and findings of the project. The report shall include the detailed design drawings and specifications, and other related information. Design drawings must be submitted in an electronic format using the current version of MicroStation.

Status: The draft final report for Phase I has been completed. A decision has been made not to proceed with Phase II. The Phase I report has been summarized in NCHRP Research Results Digest 273.

Product Availability: The draft final report is available for loan from the NCHRP.

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