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June 23, 2005

In Reply Refer To: HSA-10/CC-92

Mr. Bill Neusch, President
Gibraltar
320 Southland Road
Burnet, Texas 78611

Dear Mr. Neusch:

In your June 7 letter to Mr. Richard Powers of my staff, you requested the Federal Highway Administration's acceptance of a cable barrier terminal designed for use with the Gibraltar Cable Barrier that was acknowledged to be a test level 3 (TL-3) barrier in my June 10 acceptance letter, B-137. With your letter, you submitted copies of crash test reports prepared by Karco Engineering and digital videos that documented the results of the crash tests that were conducted on the new terminal.

Your cable barrier terminal consists of a cable release anchor post and four terminal posts, the first of which is set 6'-3 beyond the anchor post, the second 6'-3 beyond the first, and the third and fourth on 7'-6 centers. These posts are then followed by standard line posts on 15-foot centers. The cable release anchor post is comprised of two HSS 2 x 4 x 3/8 steel posts welded to a ¾-inch thick steel base plate. This anchor post rests on a 1/2-inch thick base plate that is welded to an HSS 8 x 8 x 3/8 tube, 30-inches long, set in a 6-foot deep x 24-inch diameter reinforced concrete foundation. This anchor post is designed to pry the cable ends out of slots in the base plate when it is struck, thus releasing all cable tension and allowing a vehicle to pass over the terminal with a relatively stable trajectory. All terminal posts are 3.25 x 2.5 C-posts, like the line posts, but the cables are held in place by 3/4-in x 5.5-in long J-bolts rather than the steel hairpins and lock plates used on the line posts. The first terminal post is angled towards the cable release post as show in Enclosure 1 and the first two terminal posts have 1.5-in diameter holes on all four sides at the ground line. All posts beyond the anchor post are set in 42-in deep reinforced concrete footings. We noted that the anchor post design was modified during the testing sequence. Specifically, the original HSS 8 x 8 x 3/8 steel anchor post was replaced with the anchor post described above for tests 3-30 and 3-34 because the larger post lodged under the impacting vehicle in earlier tests, causing the small car to overturn. The original post remained intact in the length-of-need test 3-35 and its release mechanism remained unchanged. Likewise, the larger post yielded satisfactorily in the reverse-direction test 3-39. Thus, I agreed that neither test needed to be conducted again with the smaller anchor post.

The National Cooperative Highway Research Program (NCHRP) Report 350 tests 3-30, 3-32, 3-35, and 3-39 were successfully conducted and the summary results of each are shown in Enclosure 2. We agreed that, upon successful results of tests 3-30 and 3-32, tests 3-31 and 3-33 could be waived for your specific terminal design. Therefore, based on the test results, the Gibraltar Cable Barrier Terminal, as described herein, may be considered an NCHRP Report 350 terminal at TL-3. In test 3-35, the pickup truck impacted the terminal at post 4 and was contained and redirected. Thus, the beginning length of need for the Gibraltar terminal is at the last terminal post, 27.5 feet downstream from the anchor post.

We noted that in test 3-30, the impacting vehicle rolled after exiting the test installation. After reviewing the film, we concluded that the vehicle had regained stability as it rode along the cable and that the rollover was the result of its wheels tripping in the loose soil at the test site rather than instability caused directly by impact into the terminal. However, this result and the post-impact trajectory seen in test 3-32 emphasize the fact that your terminal, like all cable terminals tested to date, has virtually no attenuating capability. Thus, vehicles impacting the end will normally continue a significant distance behind and beyond the barrier and are then likely to encounter non-traversable terrain or other roadside hazards or encroach into opposing traffic lanes when the barrier is used in a median. Designers must take this fact into account when selecting an optimum location for terminals in the field.

Please note also the following standard provisions that apply to the FHWA letters of acceptance:

Sincerely yours,


/original signed by/

John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety

2 Enclosures


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