Federal Highway Administration
September 9, 2005
In Reply Refer To: HSA-10/B-137A
Mr. Bill Neusch, President
320 Southland Road
Burnet, Texas 78611
Dear Mr. Neusch:
In your August 11 letter to Mr. Richard Powers of my staff, you requested the Federal Highway Administration's (FHWA) acceptance of a modified version of your TL-3 Gibraltar cable barrier system that was tested to the NCHRP Report 350 test level 4 (TL-4). Copies of the August 5 report prepared by Exponent Failure Analysis Associates in Phoenix, Arizona entitled "NCHRP Report 350 Test 4-12 of the Gibraltar Longitudinal Cable Barrier System" and digital videos of the test were also submitted.
Your modified cable barrier system consists of three, 3/4-inch diameter 3 X 7 post-tensioned galvanized steel cables supported by steel C-posts 3.25 x 2.5 x 0.15-inches thick and 7-ft long, The posts, set on 14-foot centers, were driven to a depth of 3.5 feet and installed on alternate sides of the cables. The 3 cables are locked in place by a 7/16-inch diameter x 24-inch long galvanized steel hairpin and lock plate that fits inside each post. For your TL-4 design, the bottom, middle, and top cable heights are set at 20 inches, 30 inches and 39 inches, respectively. These details are shown in Enclosure 1, which also includes drawings of the terminal. This terminal is essentially identical to the TL-3 design developed for use with the original TL-3 Gibraltar Cable Barrier. The only modification needed in the terminal to match the higher cables in the TL-4 barrier design was the increased height of the center and top cables at terminal post 4. The barrier test installation was 350 feet long and each cable was tensioned to 4800 lbs. prior to the tests.
The NCHRP Report 350 test 4-12 was successfully conducted and the summary results are shown in Enclosure 2. Dynamic deflection was reported to be 7 feet in the 350-foot long test installation. Since the bottom cable remained at the same height as the TL-3 design, we agreed beforehand that tests with the small car and the pickup truck could be waived. Based on the test results, the Gibraltar Cable Barrier as described herein may be considered an NCHRP Report 350 TL-4 median barrier when the posts are set on alternate sides of the cables or as a TL-4 roadside barrier when the cables are all on the traffic side of the C-posts. Shorter, socketed line posts, as shown in the enclosed drawing may be used in lieu of driven posts.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
(Original Signed by)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety
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