October 20, 2005
Refer to: HSA-10/CC-64F
Mr. Albert W. Unrath Sr.
Albert W. Unrath, Inc.
P.O. Box 317
Line Lexington, Pennsylvania 18932-0317
Dear Mr. Unrath:
In my December 21, 2004, acceptance letter, CC-64E, your 198-cm (78-in) long U-MAD truck mounted attenuator (TMA) was recognized as a test level 2 (TL-2) TMA acceptable for use on the National Highway System (NHS). This acceptance was based on the successful completion of the TMA tests 2-50 and 2-51. On September 30, 2005, you sent a letter to Mr. Richard Powers' attention, requesting the FHWA's confirmation that this same unit also meets the NCHRP Report 350 evaluation criteria for optional TMA tests 2-52 and 2-53.
To support your request, you sent copies of two test reports prepared by the Transportation Research Center at East Liberty, Ohio, entitled "NCHRP Report 350 Test 2-53 of the U-MAD 70K Truck Mounted Attenuator - TRC Inc. Test Number: 050728-1", and NCHRP Report 350 Test 2-52 of the U-MAD 70K Truck Mounted Attenuator - TRC Inc. Test Number: 050728-2", both dated July-August 2005. In test 2-53, a 2000-kg pickup truck impacted the TMA at a 10-degree angle relative to the TMA centerline and offset 1/4 of the vehicle width. The impact speed was 67.0 km/h. The occupant impact velocity was reported to be 10.0 m/sec and the ridedown acceleration 11.9 g's. The 9003.8 kg support vehicle rolled ahead 3.2 meters. In test 2-52, the pickup truck impacted the TMA at zero degrees and offset 1/3 of the vehicle width. The impact speed in this test was 67.1 km/h. The occupant impact velocity was reported to be 10.5 m/sec and the ridedown acceleration 15.6 g's. The support vehicle rolled ahead 3.3 meters. You noted that in both tests, the impacting vehicle came to rest in contact with the crushed TMA with a yaw angle less than 10 degrees, thus making it unlikely that the pickup truck would have blocked adjacent traffic lanes.
I agree that your 198-cm (78-inch) long TL-2 U-MAD has now been shown to meet Report 350 evaluation criteria for the two optional TMA tests and may continue to be used on the NHS when such use is deemed appropriate by the contracting authority. It was noted that neither test report contained a dimensioned drawing of the TL-2 unit in the body of the report and that the separate drawing that was sent showed an incorrect length of only 183 cm (72 inches). Please resubmit a corrected drawing at your earliest convenience.
The following standard provisions that apply to the FHWA letters of acceptance were included in the original acceptance letter, but are repeated below for ready reference:
/original signed by George Ed Rice, Jr./
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety
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