March 10, 1988
Refer to: HNG-14/SS-06
Mr. Albert M. Moreno, Sr.
Minute Man Anchors, Inc.
305 West Walker Street
East Flat Rock, North Carolina 25726
Dear Mr. Moore:
Your December 28, 1987, letter requested Federal Highway Administration (FHWA) approval of a modified breakaway device for use with flanged steel sign supports. My January 29th reply expressed concern that the modified device was substantially different from a previously accepted design and that crash testing the new device was recommended to verify it’s impact performance.
On February 26 you sent a copy of a report showing that the new device performed acceptably in a 20 m.p.h pendulum test conducted by Southwest Research Institute. When extrapolated to 60 m.p.h using the procedure currently endorsed by FHWA, the results were also satisfactory. The changes in velocity for the 1,800 pendulum were 5.8 and 2.7 feet per second for the 20 m.p.h. (actual) and 60 m.p.h. (extrapolated) conditions, respectively. These results are below the current AASHTO breakaway specifications of 10 feet per second (desirable) and 15 feet per second (acceptable).
Based on the above information, the breakaway device sown on Drawing No. MMB-1 (copy enclosed) with revisions dated 12/15/87 and 1/26/88 is acceptable for use on Federal-aid projects if proposed by a State highway agency. Our calculations indicate that two such breakaway devices within an 8-foot path would produce a 13.8 feet per second change in velocity, thus meeting the maximum acceptable value of 15 feet per second.
The FHWA acceptance is limited to the breakaway characteristics of the system and does not cover its structural features. We assume that you will provide potential users with sufficient information on structural design and installation requirements to ensure proper support performance.
L. A. Staron, Chief
Federal-Aid and Design Division
copies to: Regional Federal Highway Administrators, w/enclosure