May 30, 2006
In Reply Refer To: HSA-10/CC-64G
Mr. Michael Kempen
Impact Absorption, Inc.
46-04 245th Street
Douglaston, NY 11362
Dear Mr. Kempen:
The Federal Highway Administration (FHWA) has previously acknowledged TL-1, TL-2, and TL-3 models of the U-MAD Truck-Mounted Attenuator (TMA) as being acceptable for use on the National Highway System. For each of these three designs, the energy-absorbing units were encased within an aluminum frame in which the top back surface was tapered down 6 inches in its last 15 inches.
In your undated letter to Mr. Richard Powers of my staff, which arrived on May 18 via Federal Express, you notified the FHWA that the manufacturer desired to replace this signature profile with a fully rectangular version. This modification would be accomplished by rotating the sloped section of the units 6 inches vertically, effectively "squaring off" the impact face. You stated that the internal energy-absorbing material would remain unchanged and that, therefore, the crash performance of the U-MAD TMA's would not change.
I agree that the proposed change in profile is not likely to affect crash performance of the U-MAD and that our earlier acceptance letters remain valid.
/original signed by/
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety