September 18, 2006
In Reply Refer To: HSA-10/CC-90A
Dean L. Sicking, P.E., Ph. D.
CEO, Safety By Design Co.
5931 The Knolls
Lincoln, NE 68512
Dear Dr. Sicking:
In my April 15, 2005, acceptance letter to you, designated as HSA-10/CC90, I accepted your Burster Energy Absorbing Technology trailer TMA as a National Cooperative Highway Research Program (NCHRP) Report 350 truck-mounted attenuator at test level 3 (TL-3) based on successful completion of the mandatory TMA tests prescribed by Report 350. On June 21, 2006, I received a request that this device also be noted as having met the two optional tests identified in Report 350. With your letter, you sent copies of test reports and videotapes documenting the results of the two optional tests.
Staff review of the optional tests you conducted on modified versions of the original design raised questions concerning the use of these tests to certify the original design as meeting the evaluation criteria for the optional tests. Furthermore, although the support vehicle was blocked to prevent forward movement in both optional tests, the rear axle was lifted off the ground and the truck shifted several feet sideways in test 3-53, casting some doubt on the validity of the test to show that there was no upper weight limit to the support vehicle. After much discussion with my staff, it was mutually agreed that you would re-run test 3-53 using the original TMA design (with the relatively minor design changes as noted below) and with the support truck fully blocked to prevent motion in any direction. We agreed to accept the results of test 3-52 if the second test 3-53 was successful.
Your August 25, 2006, letter to Mr. Richard Powers of my staff transmitted the results of your second test. Enclosure 1 shows a drawing of your final design. You reported that this design differs from the originally accepted version in that the 1) the bolted splice in the middle of the first stage energy absorbing tube has been moved to the junction between the second and third stages and 2) the third stage energy absorbing tubes were scored over the first 305 mm (12 inches). Enclosures 2A-2C are the test summary sheets for test 3-52, the first 3-53 test, and the final 3-53 test on the modified original design, respectively.
I agree that the final design may be considered to meet all four Report 350 TMA tests and may be used with a support vehicle with no upper weight limit. Since the lowest acceptable weight limit has not been established through testing, it remains the manufacturer's responsibility to advise potential users of the TMA as to what lower limit is appropriate to ensure the safety of occupants of an impacting vehicle, the driver of the support truck, and other motorists and workers in the immediate area. Primary concerns with the use of a relatively light (and untested) support vehicle are the unknown post-crash stabilities and trajectories of both the impacting vehicle and the support truck.
Please note that the standard provisions to the Federal Highway Administration acceptance letters included in our original letter remain applicable to this modification as well.
/original signed by/
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety