Refer to: HSA-10/SS-122
Mr. Ron Riker
103 Regent Drive
Brownwood, Texas 76801
Dear Mr. Riker:
Thank you for your letter of December 15, 2003, requesting Federal Highway Administration (FHWA) advice on testing your company's Shur-Tite © socket system as a breakaway mechanism for rural mailbox supports for use on the National Highway System (NHS) under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features." You provided video documentation of bogie vehicle testing and static pull testing, and asked if a pendulum test would be adequate to prove the breakaway performance of the mailbox support.
The Caminoverde Shur-Tite© socket system consists of a 3-inch diameter, 17-inch long pipe socket in a concrete footing. The socket is fabricated with a hole near the toe to permit concrete to flow in, locking the socket into place. The 2-3/8-inch signpost is then placed into the socket and secured into place with a wedge of high density polyethylene. The breakaway sign support system was tested with a fiberglass post and with an ASTM 1011 Grade 55 steel post. On July 10, 2003, we found the breakaway sign support system acceptable in our Acceptance Letter SS-117.
The Shur-Tite® Mailbox Bracket is shown in the enclosed drawing for reference. It is formed from a sheet to 0.074 inch 14 gage A36 steel. A pair of downwardly extending flanges are formed on the long edges of the plate. The flanges have holes to facilitate attachment to the mailbox, and additional holes reduce the weight of the bracket. A cylindrical sleeve of 1020 steel with a 2.5 inch OD by 0.065 inch wall is wire welded to the plate forming a socket to receive the post. A 5/16" bolt secures the bracket to the post through holes on both sides of the sleeve and the support post.
The Shur-Tite® Support Post is composed of a recycled HDTP/tire rubber composite with a co-extruded HDTP white shell coating. The OD of the post is 2.375 inch with a wall thickness of 0.450 to 0.475 inch.
We agree that a single pendulum test would be adequate to demonstrate the satisfactory breakaway performance of the Shur-Tite® Socket System in a mailbox support. However, we have also compared the Shur-Tite® mailbox installation to other conventional mailbox supports such as the 4x4 wood post. We consider a Type A rural mailbox attached to a 4x4 post, a very common and inexpensive system nationwide, to be minimally acceptable from a crashworthy standpoint. We believe that you have already demonstrated superior performance of the Shur-Tite® system to the 4x4 wood post and have decided to find it acceptable for use with a mailbox no heavier than that used in the bogie test.
The results of testing met FHWA requirements and, therefore, the devices described above and shown in the enclosed drawings for reference are acceptable for use as Test Level 3 devices on NHS under the range of conditions tested, when proposed by a State. Should you wish to use the Shur-Tite® system with multiple mailboxes, or with heavier, more secure mailboxes, then full-scale high-speed crash testing would be required.
Please note the following standard provisions that apply to FHWA letters of acceptance:
(Original Signed By R. Powers)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety