February 8, 1995
Refer to: HNG-14/SS-52
Mr. Nick D. Calvi
Allied Highway Sales
9651 West 153rd Street
Orland Park, Illinois 60462
Dear Mr. Calvi:
Thank you for your letter of January 11 requesting the Federal Highway Administration's acceptance of sign installations consisting of three of your company's 63.5-mm square, 2.7-mm thick wall (2 ½ inch square, 12 gage wall) steel posts mounted on three-bolt slip-bases. On May 1, 1991, in a letter to Unistrut Corporation (copy enclosed) we found the three-bolt slip-base for square steel tube posts acceptable. The crash-tested design used three supports, each consisting of 44.5-mm (1 ¾ inch) tubes inside 50.8-mm (2 inch) tubes, with the bases mounted in concrete. The hardware shown in your drawings is essentially the same as that of the Unistrut three-bolt slip-base sign supports, with the exception that you propose to offer the option to use a galvanized steel bolt retainer (keeper plate), where Unistrut specifies a Teflon bolt retainer, which is the only type bolt retainer that was successfully crash-tested. The friction reducing Teflon keeper plate is a distinctive feature of the tested base and may be essential to the base's proper performance.
Thus, except for the use of the galvanized steel keeper plate, which would have to be qualified through crash testing, if you can verify that the hardware is essentially the same as that upon which our acceptance was given to Unistrut, your slip-base will be acceptable for use on the National Highway System, subject to the conditions set forth in our May 1, 1991, letter to Unistrut, if requested by a State high agency. However, we would point out that it is our understanding that Unistrut holds a patent on it's slip-base, which you may wish to investigate to avoid a patent infringement.
Jerry L. Poston, Chief
Federal-Aid and Design Division
Geometric and Roadside Design Acceptance Letter SS-52