April 25, 1995
Refer to: HNG-14/SS-17B
Mr. Tauhid Husain
Transpo Industries, Inc.
20 Jones Street
New Rochelle, New York 10801-6024
Dear Mr. Husain:
In our March 7 letter to you we accepted the Transpo "Type A" Break-Safe sign support system for use with square steel tubes. During a telephone conversation with Mr. Nicholas Artimovich of my office you asked why we limited our acceptance to a single support within a 2.1-meter span. You cited on January 8, 1990, letter, which previously accepted dual supports on Type A couplings. The Type A couplings were tested twice using a pendulum, first with a standard structural shape and then with a back-to-back u-channel post, with acceptable results. Because the results were so favorable we extended acceptance of all of the tested couplers to permit two posts within the 2.1-meter span.
During the testing of small and large sing supports study that ended in 1992, we saw some failures of multiple post supports that had been thought to be crashworthy. Since your original request did not specify the number of posts in a support system for which you sought acceptance we put the condition in our March 7 letter limiting the use of Type A couplings with square tube supports to no more than one within a 2.1-meter span.
Upon further review we have concluded that the square tube supports will perform as well as, if not better than, the wide-flange and back-to-back u-channel posts that were previously accepted. Therefore, consistent with our 1990 acceptance of Type A couplings within a 2.1-meter span, two square steel tube sign supports mounted on your company’s Type A couplings will be acceptable for use on the National Highway System if requested by a State. The other conditions contained in our March 7 letter are still applicable.
Jerry L. Poston, Chief
Federal-Aid and Design Division
Additional Supplement to Geometric and Roadside Design Acceptance Letter Number SS-17