Federal Highway Administration
400 Seventh St., S.W.
Washington, D.C. 20590
May 2, 2006
In Reply Refer To:HSA-10/B-141A
Mr. Stephen L. Brown
Trinity Highway Safety Products, Inc.
P.O. Box 568887
Dallas, Texas 75356-8887
Dear Mr. Brown:
In my November 17, 2005, acceptance letter B-141, I agreed that a 3-rope CASS cable barrier using weakened S4 x 7.7 structural steel posts set in concrete footings on 20-foot centers met the National Cooperative Highway Research Program (NCHRP) Report 350 evaluation criteria as a test level 3 (TL-3) traffic barrier. While I also agreed that the same system with direct-driven posts would likely meet Report 350 criteria, I stated that testing would need to be done to determine the design deflections for alternative post designs. The Texas Transportation Institute conducted a test on the system described below on February 6, 2006, and detailed the results in its April 2006 report, "NCHRP Report 350 Test 3-11 of the CASS-TL3 with Driven Posts Spaced at 20 Ft."
In his April 21, 2006, letter, Mr. Brian Smith sent copies of this report to Mr. Richard Powers and requested the Federal Highway Administration's (FHWA) acceptance of the TL-3 modified CASS design which used 6-foot long, direct driven S4 x 7.7 steel posts on 20-foot centers. The 3/4-inch diameter cables were set at the same heights as in the earlier test (i.e., 21.0, 25.2, and 29.5 inches above the ground surface, measured to the center of each cable). The posts were again weakened by adding two 11/16-inch diameter holes through each flange at ground line as shown in the enclosure to this letter, and were driven to a depth of approximately 39 inches. The cables were not pre-stretched, but were tensioned to 5,600 pounds force for the test. The dynamic deflection for the 334-foot long test installation was 6.2 feet. By comparison, the deflection for the socketed posts in your earlier test was 7.7 feet.
The CASS TL-3 design described above may be used as either a roadside or median barrier on the National Highway System (NHS) when such use is acceptable to the contracting agency. Although the cables used in the test were not pre-stretched, this acceptance is also valid if and when pre-stretched cables are used, assuming that the recommended post-tensioning is applied to the barrier.
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
Safety Home | FHWA Home | Feedback