June 9, 2005
In Reply Refer To: HSA-10/CC-91
Mr. Dallas James
PO Box 303 177
North Harbour, Aukland, 1330, New Zealand
Dear Mr. James:
In your April 12 letter, you requested Federal Highway Administration acceptance of a W-beam guardrail terminal called the X350 as an National Cooperative Highway Research Program (NCHRP) Report 350 test level 3 (TL-3) design. To support this request, you sent me a March 2005 report prepared by the University of Canterbury in Christchurch, New Zealand, entitled “Armorflex X350 Redirective, Non-gating Guardrail Terminal End,” system drawings, and digital videos of the crash tests that were conducted. Specific questions raised by my staff concerning the test vehicle specifications were adequately addressed in Dr. Chris Allington's June 3 letter response.
The Armorflex X350 terminal is designed for use with strong-post W-beam guardrail. Its unique design features include an impact head through which two anchor cables are threaded, breakaway line posts, a slider/slider bracket assembly, a cable anchor bracket, and a foundation anchor. Enclosure 1 shows the general layout of this 1143-cm long terminal and isometric views of its traffic and field sides. For side impacts, tension in the rail is transferred via the cables to the foundation anchor to provide containment and redirection. For head-on and angled impacts directly at the end, friction between the cables and the impact head dissipates crash energy and the slider/slider bracket assembly allows the first W-beam rail segment to slide back along the second segment and away from the impacting vehicle. To verify the crashworthiness of the X350, six NCHRP Report 350 tests were conducted, the summary sheets for each of which are shown in Enclosure 2.
Tests 3-30, 3-31, 3-32, 3-33, and 3-39 are standard tests for barrier terminals and crash cushions. Typically, W-beam terminals are also subjected to test 3-34 at the designated critical impact point (CIP) and test 3-35 to determine the beginning of the length of need (LON) for the barrier. However, since the X350 was believed to have redirectional capability from just beyond the first post, you ran test 3-37 to verify the terminal's assumed performance when impacted immediately downstream from post 1. The successful results of test 3-37 indicated that the CIP point and the beginning LON point are at the same location for your terminal, making tests 3-34 and 3-35 redundant and, therefore, unnecessary. Based on the post-crash trajectories of the vehicles in tests 3-32 and 3-33, the X350 must be classified as a gating terminal requiring a reasonable runout area behind it. Unlike current W-beam terminals, however, the X350 terminal has redirectional capability from the first post as demonstrated in test 3-37. Thus, the barrier length of need may be measured from the first post when this terminal is used.
Based on staff review of your submission, I agree that the X350 W-beam terminal meets the appropriate evaluation criteria for an NCHRP Report 350 terminal at TL-3. I also agree that this design would be equally crashworthy if standard CRT posts were used in post positions 2 through 6 in lieu of your proprietary steel post design. If you plan to market this product in the United States (U.S.), all steel components must be manufactured in this country with U.S. steel, pursuant to the provisions of Title 23, Code of federal Regulations, Section 435.610. Likewise, the use of proprietary products on federally funded projects is subject to the provisions of Section 435.611 of the same Regulations. Copies of both documents are available upon your request.
Please note the following standard provisions that apply to the FHWA letters of acceptance: