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U.S. Department of Transportation

Federal Highway Administration

400 Seventh St., S.W.
Washington, D.C. 20590

November 3, 2005

In Reply Refer To:HSA-10/B-140

Mr. Steve L. Brown
President
Trinity Highway Safety Products Division
P.O. Box 568887
Dallas, Texas 75356-8887

Dear Mr. Brown:

In his September 19, 2005, letter to Mr. Richard Powers, Mr. Don Johnson requested the Federal Highway Administration (FHWA) acceptance of a new strong post W-beam guardrail design called the T-31. With the letter, he also sent copies of a Texas Transportation Institute (TTI) report dated September 2005, entitled "NCHRP Report 350 TL-3 Testing of the T-31 W-beam Guardrail", and videotapes of the two tests that were conducted. Both of these tests were run using the new test vehicles that are being proposed as replacements for the 820C and 2000P vehicles in the ongoing National Cooperative Highway Research Program (NCHRP) project to update to Report 350. Specifically, test 3-10 was conducted using a car weighing approximately 1100 kg impacting the barrier at a 25-degree angle and test 3-11 was conducted with a quad-cab pickup truck with a nominal weight of 2270 kg.

The T-31 guardrail uses standard 12-gauge W-beam panels mounted on modified W6 x 8.5 steel posts with a top-of-rail height of 31 inches. The modified posts, called SYLP (Steel Yielding Line Posts) posts are 6-feet long and set in the ground to a depth of 40 inches. Each post has four 13/16-inch diameter holes in the flanges at the ground line. The rail is attached to each post without an offset block using a 5/8-inch diameter x 1-3/4-inch long special bolt with a slotted countersunk head. A 6-inch long section of W-beam called a flange protector (backup plate) is used at each post. All splices in the W-beam rail elements fall midspan, between adjacent posts. Design details for the SYLP post and its unique connection bolt are shown on Enclosure 1.

As noted above, the T-31 was first tested using the heavier vehicles (and the increased impact angle for the small car) that are proposed for use in the Report 350 update that is currently nearing completion. However, after reviewing the results of the two tests you ran under the proposed guidelines and realizing that it will be several years before any new guidelines become effective, my staff concluded that the current small car test could be more critical than the anticipated future test 3-10. Specifically, it was thought that a lighter small car impacting at the standard 20-degree angle would have contact with more of the T-31 support posts than occurred in your test with the heavier car at the 25-degree impact angle. Consequently, on October 19, 2005, the TTI conducted the standard car test and sent the summary results to Mr. Powers on October 26, 2005. Although the occupant impact velocities and ridedown accelerations were somewhat higher in the second test, all values remained under the NCHRP Report 350 preferred limits. There was less rail deflection with the shallower impact angle but more damage to the vehicle itself. Summary sheets for each of the three tests are shown as Enclosure 2.

Based on these test results, the T-31 barrier system as described above is classified as a test level 3 barrier and may be used on the National Highway System when such use is acceptable to the contracting authority. The T-31 guardrail may be considered crashworthy under both the existing Report 350 guidelines and under the new guidelines when they are formally adopted, assuming that the test matrix currently being proposed by the researchers remains unchanged.

Please note 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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