CHAPTER 7

Research Summary

7.1 Overview

This chapter outlines the research activities undertaken to develop a recommended HTCB Acceptance Plan. The recommended HTCB Acceptance Plan serves as a standalone document that state DOTs and other transportation agencies can reference when developing specifications for HTCB projects. It standardizes various aspects of HTCB implementation, including project bidding, design specifications, installation, maintenance, and training.

7.1.1 Research Approach

The following is a concise outline of the general tasks that were completed while developing the recommended HTCB Acceptance Plan, which can be found in Appendix A. More detail and discussion of each task is presented in the following sections.

• Assemble the recommended HTCB Acceptance Plan:
  • – Introduction
  • – HTCB Terminology
  • – Manufacturer and System Information
  • – Materials
  • – Material Testing
  • – Geotechnical Analysis for HTCB In-Ground Structures
  • – Site Design Considerations
  • – Installation and Maintenance Considerations
  • – Guidance for HTCB Training
• Peer Review the Recommended HTCB Acceptance Plan
• Propose Changes to AASHTO M 30

7.2 Assembly of the Recommended HTCB Acceptance Plan

The recommended HTCB Acceptance Plan consists of the topics that were approved by the project panel. The following subsections detail the research approach and scope of work for each of the six proposed subject areas for the recommended HTCB Acceptance Plan. These research areas and topics are based on details from the scope of work and research performed during the literature review, the survey of states, and manufacturer interviews.

7.2.1 Introduction and HTCB Terminology

Section 1 of the recommended HTCB Acceptance Plan contains an introduction and description of the scope of the document. Section 2 of the recommended HTCB Acceptance Plan lists

the definitions of common HTCB-related terms along with abbreviations used in the document. The terminology is split into four sections: (1) national standard-setting organization terms, (2) general cable barrier terms, (3) geotechnical terms, and (4) manufacturer-specific terms.

7.2.2 Manufacturer and System Information

Section 3 of the recommended HTCB Acceptance Plan provides a comprehensive overview of HTCB design principles and system characteristics. While initially detailed specifications of existing HTCB systems were included, the peer review process (described in Section 7.3) led to a more generalized approach to ensure long-term relevance as systems evolve and new products emerge. This section identifies current HTCB manufacturers but directs readers to the Federal Highway Administration’s eligibility letter website for current product specifications. It also explores both the fundamental operating principles of cable barrier systems and the various cable release mechanisms employed in current designs.

The opening three sections of the Acceptance Plan are designed to provide readers with the technical foundation necessary to make informed barrier selections based on their specific application requirements and site constraints.

7.2.3 Materials and Material Testing

Section 4 of the recommended HTCB Acceptance Plan addresses common materials and components across all HTCB systems, including high-strength galvanized wire rope, turnbuckles, and tensioning hardware, galvanizing standards, and concrete specifications. Rather than prescribing specific approved materials, this section serves as a general reference guide. Information on the potential use of stainless-steel cable was excluded from the acceptance plan document; however, the research findings on this topic are presented in Section 2.5.7. Similarly, material types for reinforcing steel in concrete anchor foundations were also excluded from the acceptance plan document, but those research findings can also be found within this report in Section 2.5.5.

Section 5 of the recommended HTCB Acceptance Plan establishes material testing protocols, detailing guidance for material identification, test documentation, and independent laboratory certification. This section aims to provide transportation agencies with confidence in testing procedures through several key elements, including

• Guidelines for quality assurance and custody control,
• Guidelines for material property certification,
• Discussion of the AASHTO Product Evaluation and Audit Solutions program, and
• Recommendations for incorporating HTCB into the AASHTO UP3 program, either through state advocacy or manufacturer initiative.

The research indicates that proper supplier quality assurance, custody control, and material certification significantly minimize the risk of non-compliant components.

7.2.4 Geotechnical Analysis for HTCB In-Ground Structures

Section 6, the most comprehensive portion of the recommended HTCB Acceptance Plan, presents detailed guidance on geotechnical sampling, analysis, and design. This section serves two primary purposes:

1. Supporting state agencies in developing well-defined project scopes that enable contractors to prepare bids based on reliable data.
2. Promoting fair competition by standardizing bid components, thus preventing artificial price reductions through understated requirements (such as insufficient soil boring quantities).

This section provides comprehensive coverage of

• Soil boring procedures, classification methods, and recommended boring frequencies;
• Geotechnical testing protocols, including soil classification, standard penetration testing, and groundwater evaluation;
• Analysis techniques for structural design, encompassing anchor foundation design using the p-y method, overturning and sliding resistance calculations, and line post footing design using Broms’ method; and
• Special considerations for anchor loading conditions, line post footing design parameters, and soil conditions (saturated and frozen).

7.2.5 Site Design Considerations

Section 7 of the recommended HTCB Acceptance Plan addresses key site design considerations for high-tension cable barrier HTCB installations. It covers common topics such as system selection and placement criteria, the use of mow strips, grading requirements at anchor foundation locations, accommodating irregular terrain along the length of need, and specifying cable height. The intent is to furnish transportation agencies with general site design guidance to enhance initial project design and scoping for HTCB projects. This section provides agencies with a framework for evaluating site-specific conditions and incorporating appropriate design measures from the outset.

7.2.6 Installation and Maintenance Considerations

Section 8 of the recommended HTCB Acceptance Plan outlines common installation methods and maintenance practices for HTCB systems. Installation topics covered include line post foundation techniques such as driven posts, driven sleeves, and concrete footers, as well as proper cable fitting procedures. Concerning HTCB maintenance, this section examines cable damage, anchor foundation movement, concrete deterioration, and protocols for verifying and adjusting cable tensions. This section promotes proper construction and upkeep of HTCB installations in accordance with recommended practices.

7.2.7 Training

The final section of the recommended HTCB Acceptance Plan, Section 9, addresses training recommendations for high-tension cable barrier systems. It outlines training topics across three key areas: (1) system installation and construction, (2) protocols for first responders, and (3) maintenance and routine inspection procedures. Given the variations between HTCB products and the training materials developed by respective manufacturers, this section furnishes a framework to enable transportation agencies to ensure contractor and personnel training programs are comprehensive and foster high-quality workmanship. Section 9 allows agencies to evaluate training curricula against the identified subject areas and skill requirements, promoting uniform expertise in HTCB deployment, incident management, and system upkeep.

7.3 Peer Review Summary

After drafting the initial recommended HTCB Acceptance Plan, the research team initiated a peer review process to gather feedback from subject matter experts. The objective of the review was to confirm that the plan

• Provides an equitable framework for all manufacturers,
• Does not impede innovation or new product development, and
• Offers useful information to transportation agencies and state DOTs.

With NCHRP approval, six subject matter experts and companies (listed in Table 33) reviewed the draft plan, providing 99 individual comments. Selected changes were then incorporated into the updated recommended HTCB Acceptance Plan.

The peer review process helped validate the plan’s fairness, flexibility, and relevance to end-users. Reviewer input strengthened the guidance to ensure it supports a competitive marketplace and continued HTCB technology advancement while meeting agencies’ needs for informed system selection and deployment.

7.4 Proposed Updates to AASHTO M 30

Current specifications from all HTCB manufacturers and transportation agencies call for a high-strength wire rope similar to AASHTO M 30 Type 1 Class A. However, as shown in Figure 7, the minimum breaking strength listed in Table 1 of AASHTO M 30 for this Type 1 wire rope is 25,000 lbf. In contrast, the ¾-inch-diameter, 3 × 7 pre-stretched high-strength wire rope used in recent HTCB crash testing and installations has a minimum breaking strength of 39,000 lbf. To reconcile this discrepancy between the breaking strength of cables used in HTCB applications and the AASHTO M 30 specification, the research team has proposed two potential update options for AASHTO M 30.

The first option is to update Table 1 of AASHTO M 30 by adding a new wire rope category, Type I(a), and defining the 39,000 lbf minimum breaking strength requirement and optional

Table 33. List of peer reviewers who received the recommended HTCB Acceptance Plan.

pre-stretching specification. This option will also require adding ISO 12076 to the referenced standards and an additional note to be placed in Table 1.

The second option is to include a Supplementary Requirement section in AASHTO M 30 that allows Type I wire rope to be specified with this higher 39,000 lbf minimum strength and optional pre-stretch specification. This option will also require a new sub-section within the Scope of M30, adding ISO 12076 to the referenced standards.

The recommended updates to AASHTO M 30 are expected to align the specification with wire rope products proven effective in modern HTCB systems, offering clearer guidance to agencies and manufacturers.