The National Academies

NCHRP 22-13 [Completed]

Performance of Roadside Barriers

  Project Data
Funds: $520,000
Research Agency: University of Iowa
Principal Investigator: Malcolm Ray
Effective Date: 4/1/1996
Completion Date: 2/28/1999

Significant improvements in highway safety have been achieved through a multitude of actions over the past three decades, but one area where serious problems still exist is the highway roadside. Crash data indicate that more than 40% of highway fatalities involve vehicles hitting objects on the roadside, including barriers. Highway designers attempt to address these roadside safety problems by minimizing the number of objects, providing adequate clear zones, or using barriers to shield the vehicles from the hazard. Several generations of barriers have been developed to improve safety, but the effectiveness of these barriers in the field is not fully understood. While crashworthiness criteria have been established in NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features," the tests are based on idealized installations of barriers. In field installations, the barrier may be located on a slope, struck at different angles, subjected to the effects of settlement, possibly installed improperly, and maintained less often than prescribed. In addition, accidents not reported to the police confound attempts to determine the true in-service performance of barriers as these may be less severe. Further, when assessing barrier performance factors such as injury risk, it is necessary to consider the changing characteristics of the vehicle fleet (e.g., airbags). These and other factors can influence in-service performance of barriers, but there has been only limited effort to investigate their effects.

Transportation agencies (federal, state, and local) need guidance on the in-service performance of traffic barriers (including permanent and temporary longitudinal barriers, crash cushions, end treatments, and breakaway supports--hereafter referred to as barriers) to make effective decisions on their use under 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 safety treatments may be needed. The RDG presents these guidelines in terms of roadside terrain, traffic volumes, design speed, accident probability, and environmental conditions. This guidance is limited to general references to applicability under specific roadside conditions because in-service performance data are inadequate. Thus, needs exist for (1) in-service performance data for roadside barriers, (2) a procedure(s) to efficiently gather these data on a regular basis, and (3) a process to compile, maintain, and share these data in efforts to improve roadside safety. Addressing these needs will make it possible to (1) develop a fuller understanding of in-service performance of barriers (e.g., impact failure modes, life-cycle costs, durability, and maintainability); (2) determine the appropriate applications of barriers in specific roadside situations; (3) improve installation and maintenance practices; (4) modify barrier and highway design standards where necessary; and (5) develop more realistic crash test criteria. These efforts will improve highway safety while recognizing the resource constraints faced by DOTs.

The objectives of this research are to (a) establish a practical procedure(s) for gathering data on the in-service performance of traffic barriers; (b) develop a viable process for compiling, maintaining, and using in-service performance data to improve roadside safety; (c) demonstrate use of the procedure(s) and process for the evaluation of a designated subset of barriers; and (d) offer recommendations for implementation of the procedure(s) and process. The procedure(s) should be comprehensive enough to apply to all common barriers and typical field applications, and a broad definition of performance is assumed.

To accomplish the project objectives, the following tasks are envisioned: (1) Review the literature and current research to assess the procedure(s) and process that have been proposed or used for in-service performance of barriers and other roadside features. Derive from this effort a comprehensive list of factors for evaluating in-service barrier performance, a categorization of barrier types and problems associated with each type, and the range and precision of data needed to evaluate barrier performance. Include a review of available data and statistical and clinical methodologies for evaluating in-service performance. (2) Contact the state agencies to determine the extent and experience of their in-service evaluations, features of safety infrastructure inventories and maintenance records, accident/risk assessment efforts, and the level of detail to which barriers are addressed in the agencies' safety management systems. (3) Conceptualize a process for compiling, analyzing, documenting, storing, and using the data for determining the in-service performance of barriers. The process should provide in-service performance data for a range of typical factors, but not necessarily for all barrier installations. (4) Establish a procedure(s) for acquiring the data necessary for in-service performance evaluation of specific barrier installations consistent with the resources available at the federal and state levels. Define the data items to be collected in the procedure (such as highway type, barrier type, exposure, side slope, offset, soil conditions, weather, vehicle type, speeds, tracking, trajectory, installation and maintenance practices and costs, occupant injury, and post-impact conditions). Consider clinical and statistical methods as appropriate. (5) Prepare a list of barrier types that may be candidates for data collection in this project. Prepare a data collection plan which includes sample size, geographic coverage, factors to be considered, sampling period, statistical analyses to be undertaken, controls for external influences, and reporting formats. (6) Prepare an interim report that details the findings and recommendations of Tasks 1 through 5 for panel approval. (7) Revise the procedure(s), process, and data collection plans based upon the guidance provided by the panel. (8) Undertake the data collection for in-service performance of the selected barriers. Train data collectors, implement appropriate quality assurance measures, document the data gathered, and provide periodic data summaries to the panel. (9) Analyze the data using the process developed in this research. Interpret the results and establish the in-service performance characteristics for the selected barriers. Provide recommendations to the panel for further revision to the procedure(s) and process. (10) Recommend a plan for the implementation of the procedure(s) and process that includes suggestions for (a) revising barrier specifications, warrants, and installation and maintenance practices as necessary; (b) appending, summarizing, and disseminating in-service performance data; (c) integrating in-service evaluations in state safety activities; and (d) promoting the process (e.g., pooled-fund studies, partnerships with industry). (11) Prepare a final report that documents the entire research effort. An executive summary highlighting the importance of in-service evaluations should be included as part of the final report.

Status: The project is complete. The preliminary draft final report has been revised to incorporate the panel's comments. Continuation funds in the amount of $280,000 have been approved for a continuation of the research effort under NCHRP Project 22-13(02).

Product Availability: The contractor's draft final report is available from the NCHRP.

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