Criteria for Restoration of Longitudinal Barriers (2010)

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1Longitudinal barriers, such as guardrails, are installed along a roadway or in the roadway median to prevent an errant vehi- cle from traversing a steep slope, impacting a more danger- ous roadside object, or entering opposing vehicle travel lanes. Full scale crash testing is used to evaluate the performance of these barriers prior to their installation along a highway (Ray and McGinnis, 1997; Ross et al, 1993). Based on an evaluation using real-world crash data, these barriers have consistently been shown to be effective (Short and Robertson, 1998; Michie and Bronstad, 1994; Elvik, 1995). Very little is known, how- ever, with respect to how these barriers perform after they have been damaged. Highway agencies expend considerable resources to repair damaged longitudinal barriers. Limited funds prevent high- way agencies from maintaining all field-installed systems in an ideal as-built condition. Instead, these agencies focus on repairing only damage that is perceived to have a detrimental effect on the safety performance of the barrier. The distinc- tion between minor damage and more severe performance- altering damage, however, is not always clear. In the case of a high severity crash involving rail penetration (left image in Figure 1), the need for barrier repair is obvious. Much more common, though, is minor barrier damage, e.g., a shallow dent which occurs in a low-speed collision or a sideswipe (right image in Figure 1). Minor damage to barriers may also result from routine highway maintenance operations, includ- ing snowplowing, mowing or paving, and exposure to the environment, which may result in corrosion or termite damage. Regardless of the cause, damage of this type poses a challenge to highway agencies. A failure to repair damage that affects barrier performance may lead to fatal consequences for pass- ing motorists as well as potential exposure of the agency to a tort liability claim. Crash testing of undamaged barriers has consistently demonstrated that seemingly insignificant alter- ations to a barrier, such as using a rectangular washer on the post-rail connection, may result in catastrophic consequences for an impacting vehicle. This underscores the importance of the ability of agencies to identify seemingly minor damage that has serious implications on crash performance. 1.1 Research Problem Statement The research problem statement for the project is quoted below: Transportation agencies expend resources to ensure that all longitudinal barriers meet the safety performance guidelines to which they were constructed. Barrier systems are damaged by a wide variety of activities and factors, including minor crashes, snow plowing, mowing operations, and deterioration due to environmental conditions. Such damage may or may not be repaired by maintenance forces. For example, snowplows often bend W-beam guardrails and sometimes bend or break the posts. Even seemingly insignificant barrier damage or deterioration may compromise a barrier’s safety performance. With limited maintenance budgets, state highway agencies often have large backlogs of needed safety-feature repairs. These agencies cannot afford to repair damage that does not alter a bar- rier’s safety performance, but significant barrier damage must be repaired to provide adequate protection for the motoring public. Unfortunately, in the absence of objective criteria for determin- ing when a repair is not required, highway agencies may be held to the unachievable standard of maintaining all safety features in as-built condition to avoid tort liability. Therefore, there is a need for objective, quantitative criteria in the form of guidelines for assessing damage and deterioration and determining when a longitudinal barrier requires repair or can remain in service. 1.2 Objectives and Scope The objective of this project was to develop guidelines to assist maintenance personnel in identifying the levels of dam- age and deterioration to longitudinal barriers that require repairs to restore operational performance. The scope of this project was limited to w-beam barriers, which are by far the most common barrier in use in the United States. The primary focus was on the barrier length of need sections. Although spe- cific end terminals were not in the scope of this project, generic guidance applicable to all end terminals was included in the recommended guidelines but was not quantitatively evaluated. It is also important to note what was not covered under the scope of this project. The guidelines pertained only to the C H A P T E R 1 Introduction

repair of damaged or deteriorated barriers and were not intended to cover installation issues such as improper instal- lation height. The project scope did not include guidelines for maintenance of cable barrier systems. Maintenance of cable systems was expected to be covered under NCHRP Project 22-25, “Development of Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems.” Rigid barriers such as the New Jersey shape concrete barrier were not in the scope of this project. Proprietary systems were also not in the scope of the project. To accomplish these objectives, the study was delineated into the following seven tasks: 1. Identify and review completed and ongoing research and activities, including international sources, related to the project objective. 2. Conduct a survey of state and Canadian provincial trans- portation agencies to gather existing policies and guide- lines governing inspection and repair of longitudinal barriers. The survey should be used to identify the barrier systems and the types of damage and deterioration that should be considered in this project. 3. Submit an interim report that, as a minimum, includes the following: • The results of Tasks 1 and 2 with a discussion of the crit- ical findings. • A discussion of the objective criteria, to be developed, for quantifying damage and deterioration related to barrier performance. • An updated, detailed work plan, including the research approach and costs to evaluate each damage and deteri- oration type identified in Task 2. • A preliminary draft outline of the proposed guidelines. 4. Meet in Washington, DC, with the NCHRP panel to review the Task 3 interim report approximately 1 month after its submittal. After the meeting, submit a revised interim report addressing the review comments and decisions at the meeting. 5. Execute the approved work plan. 6. Submit the preliminary draft guidelines for review by the panel. Revise the guidelines addressing the review comments. 7. Submit a final report documenting the entire research effort. The final report shall describe how the project was conducted and include an appendix with the guidelines. 1.3 Organization of Report The first chapter presents the critical need to establish quan- titative guidelines and criteria for the repair of longitudinal barriers and the research statement for NCHRP Project 22-23. Chapter 2 first presents a synthesis of the current repair cri- teria for longitudinal barriers with crash damage or environ- mental deterioration. Chapter 3 presents the research team’s approach to evaluating the crash performance of longitudinal barrier with minor damage modes. This chapter describes each of the three evaluation approaches, i.e., pendulum testing, full scale crash testing, and computational modeling. Chap- ters 4–14 present the results of the evaluation of the crash performance of longitudinal barriers with minor damage and the recommended repair criteria and the rationale for each criterion. Chapter 15 presents a summary of the rec- ommended repair guidelines. Finally, Chapter 16 presents the final product—a “Field Guide for Criteria for Restoration of Longitudinal Barriers.” A comprehensive set of appendices are provided which include all test reports and a detailed report on the finite element simulations. 2 Figure 1. Catastrophic vs. minor guardrail damage.