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                Safety Eligibility Letter B-137
  
  **Hardware Type:**
            Longitudinal Barriers and Bridge Rails
                          **Code:**
            B-137
                          **Date:**
            06/13/2005
                          **Testing Criteria:**
            NCHRP 350
                          **Manufacturer:**
            Gibraltar
                          **Device Description:**
            Gibraltar cable barrier @ TL-3
                          **View PDF:**
            b137.pdf (244.27 KB)
    
    
Skip to contentUnited States Department of Transportation - Federal Highway AdministrationJune 13, 2005
In Reply Refer To: HSA-10/B-137
Mr. Bill Neusch, President
	Gibraltar
	320 Southland Road
	Burnet, Texas  78611
Dear Mr. Neusch:
In your May 30 letter to Mr. Richard Powers of my staff, you requested the Federal Highway Administration (FHWA) acceptance of a high-tension, 3-strand cable barrier system. Copies of a May 26 report prepared by Karco Engineering and entitled “Crash Test Report for Gibraltar Tested to National Cooperative Highway Research Program (NCHRP) Report 350 Recommendations for test level 3-10 and 3-11 Cable Barrier System” and digital videos of the two tests were also submitted.
Your cable barrier system consists of three 3⁄4-inch 3 X 7 prestretched, post-tensioned galvanized steel cables supported by steel C-posts 3.25 x 2.5 x 0.15-inches thick and 4-ft long, set in HSS 4 x 3 x 3/16 sockets.  These sockets were 15-inches deep and placed in reinforced concrete footings 42-inches deep and 12-inches in diameter.  Post spacing was 15 feet on centers.  The posts were installed on alternate sides of the 3 cables that are held in place by a 7/16-inch diameter x 24-inch long galvanized steel hairpin and lock plate, with which the bottom, middle, and top cable heights are set and held in place at above-ground heights of 
20 inches, 25 inches and 30 inches, respectively.  These details for the line posts are shown in Enclosure 1.  This enclosure also includes drawings of the terminal you developed for use with the Gibraltar Cable Barrier, which will be addressed in a separate acceptance letter in the immediate future.  The barrier test installation was 200 feet long and each cable was tensioned to 4800 lbs. prior to the tests.
The NCHRP Report 350 tests 3-10 and 3-11 were both successfully conducted and the summary results of each are shown in Enclosure 2.  Dynamic deflection was reported to be 
8.5 feet.  Based on the test results, the Gibraltar Cable Barrier may be considered an NCHRP Report 350 traffic barrier at test level 3 as a median barrier when the posts are set an alternate sides of the cables or as a roadside barrier when the cables are all on the traffic side of the 
C-posts.
You also asked about the acceptability of an alternative post embedment detail and the effect additional tension in the cables might have on the dynamic deflection of your barrier.  Regarding post embedment details, a 30-inch deep reinforced concrete footing can be used when a mowing strip is used under the barrier.  While longer posts embedded directly into the ground would almost certainly work, other factors such as post type and spacing, the use of soil plates, soil conditions, the distance between adjacent terminals or anchors, and the method used to connect the cables to the posts will affect the deflection distance and there is currently no way to predict that deflection with any degree of confidence.  Similarly, increasing the cable tension will intuitively decrease deflection, but any such decrease cannot be readily quantified as it, too, is dependent on the factors listed above.  To determine the design deflections for alternative post designs or post spacing, testing would need to be done.  Design deflections for longitudinal barriers are only a reasonable approximation of what may be seen in the field. Because they are the observed results of a single test, actual deflections for any specific barrier can be much more or much less, depending on the size, speed, and impact angle of the vehicle that strikes it.  In locations where deflection is a critical design element, a rigid concrete barrier would be a more logical choice than a flexible or semi-flexible barrier type.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
Our acceptance is limited to the crashworthiness characteristics of the tested device and does not cover its structural features, durability, or maintenance characteristics.
Any design or material changes that may adversely affect the crashworthiness of the barrier will require a new acceptance letter.
Should the FHWA discover that the qualification testing was flawed, that in-service performance reveals unacceptable safety problems, or that the barrier being marketed is significantly different from the version that was crash tested, it reserves the right to modify or revoke its acceptance.
You will be expected to supply potential users with sufficient information on design and installation requirements to ensure proper performance.
You will be expected to certify to potential users that the hardware furnished has essentially the same chemistry, mechanical properties, and geometry as that submitted for acceptance, and that they will meet the crashworthiness requirements of the FHWA and the NCHRP Report 350.
To prevent misunderstanding by others, this letter of acceptance, designated as number B-137 shall not be reproduced except in full.  This letter, and the test documentation upon which this letter is based, is public information.  All such letters and documentation may be reviewed at our office upon request.
The Gibraltar Cable Barrier includes patented components and is considered proprietary.   When proprietary devices are *specified by a highway agency* for use on Federal-aid projects, except exempt, non-NHS projects, they: (a) must be supplied through competitive bidding with equally suitable unpatented items; (b) the highway agency must certify that they are essential for synchronization with existing highway facilities or that no equally suitable alternative exists or; (c) they must be used for research or for a distinctive type of construction on relatively short sections of road for experimental purposes.  Our regulations concerning proprietary products are contained in Title 23, Code of Federal Regulations, Section 635.411.Sincerely yours,
/original signed by/
John R. Baxter, P.E.   
						Director, Office of Safety Design 
						Office of Safety
2 Enclosures
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