CHAPTER 4

Summary of Manufacturer Interviews

The research team conducted interviews with four HTCB manufacturers. Each interview lasted between 60 and 90 minutes and followed a conversational format. The topics covered during the interviews included challenges for the manufacturers, soil testing, line post footer design, anchor foundation design, cable and fittings, manufacture/testing of components, and training. The results of the interviews are synthesized in the following sections of this chapter.

4.1 Challenges for the Manufacturers

During the interviews, one of the primary concerns raised by cable barrier manufacturers was the potential challenge posed by the proprietary nature of HTCB systems. They unanimously stressed the importance of ensuring any guidelines or acceptance plans developed in this project maintain fair competition, allowing all manufacturers equal opportunity to bid on projects.

Manufacturers cautioned that certain state standard specifications, including minimum post spacing, sleeve material type, or component material requirements, could inadvertently favor some products while excluding others. This could potentially restrict competition by excluding certain manufacturers from bidding.

Manufacturers expressed concern about potentially overly restrictive guidelines from this project. They prefer guidance for transportation agencies to primarily follow “manufacturer requirements” or “as-tested” design and installation specifications, aiming to minimize modifications to HTCB designs.

In conclusion, manufacturers have invested substantial time and resources to develop, validate, and test their HTCB systems. They caution that state-mandated changes to specific components, materials, or designs of tested systems may affect performance in unforeseen ways, potentially leading to unintended consequences.

4.2 Geotechnical Analysis

Geotechnical analysis plays a crucial role in the selection and design of anchor foundations and line post embedment/footers for HTCB systems.

Multiple manufacturers observed that HTCB crash testing only assesses the barrier’s above-ground components, excluding subsurface structures. Based on this feedback, the research team concluded that the standardized soil conditions specified by MASH for full-scale testing typically create rigid or semi-rigid boundary conditions, where minimal displacement occurs at post footings and end anchor foundations. Therefore, foundation designs for actual field installations must be engineered to achieve comparable strength and rigidity characteristics.

All four HTCB manufacturers use external consultants for the design of anchor foundations and line post footers. The geotechnical analysis typically includes standard penetration tests soil type classification, water table depth, frost depth, and soil borings up to 15 feet deep. For soil strength calculations, the Broms’ method and the p-y method are applied.

Some manufacturers acknowledged the potential benefits of standardizing agency requirements for geotechnical analysis, including details on boring frequency, variable assumptions, and factors of safety.

4.3 Line Post Footer Design

Line post installation typically employs one of three methods: (1) driven posts, (2) posts set in driven sockets, or (3) posts installed in plastic or steel sleeves within concrete footings. Regional preferences vary, particularly in areas with severe winters where frost heaving is a concern. In these regions, driven posts or sockets are often preferred since they can be easily re-driven if displaced by frost.

Mow strips used with concrete line post footers have become increasingly popular in recent years. Mow strips add additional lateral support to the line post footers, which reduces the amount of cracking and footer displacement that can be experienced during a crash. Anecdotally, there seems to be evidence that by “pinning” the mow strip down at every post, there can be more rigidity in the mow strip, which results in greater resistance to buckling or frost heaving. This beneficial interaction between the mow strip and footings represents an interesting structural relationship.

When reinforced concrete mow strips are used in conjunction with concrete line post footings, manufacturers’ standard footing designs typically provide adequate performance, with reduced instances of footing displacement and concrete deterioration.

A geographical demarcation could potentially be established, where mow strips might serve as an appropriate design feature south of this boundary, while driven post or socket designs may be more suitable in northern regions because of frost heave concerns.

As previously discussed, standardizing the Broms’ method for calculating lateral capacity of line post footings across the industry could prove beneficial. Additionally, adopting a uniform factor of safety of 1.5 for these calculations may be appropriate.

4.4 Anchor Foundation Design

Anchor foundation designs are typically based on the maximum cable tension at the historical low temperature for the location where the system is installed, as well as the cyclical thermal loading that occurs throughout the year.

For a particular project, some states allow for the design of one or two typical anchors, based on worst-case site conditions. Other states require that each anchor on a project be designed specifically for the soil conditions at each anchor site. The manufacturers prefer jobs where typical anchor designs can be used.

Some states design anchor foundations for super-saturated soils (e.g., low soil strength) rather than for extreme cold conditions (e.g., those that cause maximum cable tension). The rationale is that during peak cable tension in low temperatures, the frozen ground provides greater lateral strength than in its thawed state.

Anchor foundation designs can be calculated using Broms’ method and the p-y method for lateral capacity and uplift resistance, respectively. These calculations could be standardized throughout the industry.

4.5 Cable and Fittings

All manufacturers of HTCB use AASHTO M 30 (ASTM A741) Type 1 Class A cable with a minimum breaking strength of 39,000 lb. This breaking strength is 56% stronger than the minimum breaking strength specified in AASHTO M 30 for Type 1 wire rope, which is listed in Table 1 of AASHTO M 30 as 25,000 lbf.

Most of the HTCB cable used in the United States is produced by a single manufacturer, but there is a second manufacturer that provides some limited amounts of cable. There has been a supply backlog of cable in the United States for a few years. One of the manufacturers has had a backlog of 6–12 million feet of cable over the last few years.

All the HTCB cable that is made in the USA is pre-stretched. There are virtually no current or recent projects using standard (i.e., unstretched) cable. There is some disagreement between HTCB manufacturers regarding the benefits of pre-stretching the cable during manufacturing, relative to how much pre-stretch advantages remain after the cable is spooled, stored, and shipped to a job.

The HTCB manufacturers use threaded connectors and turnbuckles with a diameter of 0.75–1.00 inches. Table 27 shows the manufacturer reported breaking strength of cables and fittings. As can be seen from Table 27, the connectors and turnbuckles have a lower breaking strength compared to the cable.

4.6 Manufacture and Testing of Components

HTCB manufacturers typically outsource the production of most system components to other mills or fabricators, while some produce posts or cable-to-post connectors.

For outsourced materials, manufacturers require suppliers to provide mill certifications and material property testing reports, as per relevant ASTM standards. This documentation is then submitted to the contractor or state before job completion.

4.7 Training

Manufacturers unanimously emphasized the importance of comprehensive training across multiple stakeholder groups. Pre-job training benefits installation crews, inspectors, and project managers. Additionally, maintenance personnel, emergency responders, towing operators, and inspection teams benefit from training conducted either during cable barrier installation or after project completion.

Effective training programs typically incorporate both classroom instruction and hands-on experience. While active installation sites can provide practical training opportunities, they present significant safety concerns. Demonstration equipment in controlled environments offers a safer alternative for hands-on learning experiences.

One manufacturer has developed a mobile application that features installation videos, procedural checklists, and tension logging capabilities. According to the manufacturer, this digital tool has received positive feedback from both customers and installation teams.

Table 27. Cable Fittings Breaking Strength.