Practices for High-Tension Cable Barriers (2016)

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5 states have developed specifications (and in some cases special provisions) addressing the design and placement of HTCB. Because these documents were developed independently, they are not consistent from state to state. This study was initiated to document existing state specifications and special provisions relating to HTCB. As noted previously, all HTCB designs currently eligible for use on public roads in the United States are proprietary. Thus, the physical design details and all material specifications have been determined by the individual manufacturers and verified through full-scale crash testing and cannot be changed or modi- fied by state DOTs. Therefore, it is important that at a minimum any state specifications address the following types of issues: • Use of HTCB, • Specific design [e.g., number of cables, Test Level (TL), length, and lateral placement], • Anchor and footing designs, and • Training requirements [DOT personnel, emergency med- ical technician (EMT), police]. SCOPE As the number of HTCB installations continues to increase, various design features and current practices can be summa- rized here to document the state of the practice and to suggest further research. The primary objective of this Synthesis study is to document existing transportation agency specifications and special provisions governing the use of HTCB in each state. Objectives include identifying warrants and design cri- teria currently used nationwide and identifying any continuing installation, construction, or maintenance areas of concern that may warrant additional study. STUDY APPROACH The development of a standardized specification for HTCB involved the following basic tasks: • Creation of a survey form for distribution to all state DOTs to ascertain the current state of the practice. • Collection and review of all materials supplied from the manufacturers of HTCB currently in use in the United States. • Review of FHWA acceptance and eligibility letters for HTCB. • Review of pertinent research efforts and selected in- service evaluation studies for HTCB. BACKGROUND High-tension cable barriers (HTCBs) are relatively inexpensive when compared with w-beam or concrete barriers and can be installed either in a median or along the outside shoulder of a highway. However, the most common applications today are in medians of divided roadways, and this synthesis will focus on that type of installation. Median cross-over crashes are typi- cally violent collisions, usually resulting in severe injuries both to occupants of the errant vehicle and to innocent persons in the opposing traffic stream. Cable barriers function by captur- ing or redirecting impacting vehicles to prevent these vehicles from intruding into the opposing traffic lanes. They are flexible systems compared with w-beam and concrete and thus deflect a greater lateral distance when impacted at high angles while at the same time reducing occupant impact forces significantly over more rigid barrier designs. Compared with other barrier types, HTCB can be installed (with limitations) on nonlevel terrain and generally requires minimal grading and drainage work. Despite more than a decade of increased use in the United States, there are still some concerns over HTCB selection, design, installation, and maintenance that need to be addressed. Although several state transportation agencies had used some type of generic low-tension cable barrier for many years, it was not until the year 2000 that a HTCB was first installed in the United States. Since then, the use of HTCB as a median barrier has spread to nearly every state in the country. Five propriety sys- tems have been deemed eligible for federal funding by FHWA, based on successful full-scale crash testing conducted under NCHRP Report 350 (Ross et al. 1993) or AASHTO Manual for Assessing Safety Hardware (MASH) guidelines. There are currently no generic HTCB systems eligible for use in the United States. Prior to 2010, these FHWA eligibility letters (formal noti- fication from FHWA that the hardware met all appropriate crite- ria and could be used on public roads) were previously referred to as acceptance or approval letters and are still referred to as such in some state departments of transportation (DOTs) specifica- tions and special provisions. The five systems currently eligible for federal reimbursement are shown in Figure 1. In addition, a more detailed description of each system, as well as manufactur- ers’ specifications for each system, can be found in Appendix C. As is the case with many new roadside safety features, lim- ited in-service performance evaluations and anecdotal evidence revealed that there were some issues with HTCB design and placement that required addressing to ensure optimal perfor- mance in the field. Consequently, several research studies were undertaken to answer some of these issues. As a result, several chapter one INTRODUCTION

6 Brifen CASS Gibraltar Nucor Safence FIGURE 1 Five high-tension cable systems.

7 • Summary of state DOT responses to survey question- naire. ORGANIZATION OF THE REPORT The information contained in this synthesis report was col- lected in several ways: a literature search, a survey of state transportation agencies, FHWA eligibility letters, and man- ufacturers’ practices, and is presented in the following chapters: • Chapter one–Introduction • Chapter two–Literature Review • Chapter three–Summary of State Survey Responses • Chapter four–Case Examples • Chapter five–Conclusions