Refer to: HSA-10/SS-68G
Mr. Lawrence E. Leahy
President, Xcessories Squared
P.O. Box 135
Auburn, IL 62615
Dear Mr. Leahy:
Thank you for your email message requesting Federal Highway Administration (FHWA) acceptance of a modification to our previous action on your company's SB10 slip base. The SB10 Slip Base was originally accepted in our letter SS-68D (February 22, 1999), and modified in letter SS-68E (December 9, 1999) as a component of a breakaway sign support system for use on the National Highway System (NHS). You requested that we find a three-post installation using the SB-10 slip base acceptable for use on the NHS under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."
Testing of breakaway supports is to conform with the guidelines contained in the NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Requirements for breakaway supports are those in the American Association of State Highway and Transportation Officials' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.
We had previously found your "SB8" breakaway slip bases acceptable for single post supports on September 18, 1996, (Geometric and Roadside Design Acceptance Letter SS-68) and for dual and triple post supports on December 20, 1996 (SS-68A). These designs used triangular plates measuring 8 inches (203 mm) on a side. We then found the identical breakaway design using
"10 inch" (254 mm) triangular slip plates acceptable by extrapolation via the letters referenced above. The larger base (the "SB10") would accommodate a 3 inch (76.2 mm) square tube sign support and was accepted for a single support installation only.
Your present request is that the SB10 base be acceptable for use under the same conditions as the SB8, that is, up to three posts (of the same maximum size and weight as permitted for the SB8 ) within a 2.1 meter span. In addition, you requested that a dual post support using the SB10 be accepted providing the weight of posts plus sign does not exceed that for the triple post SB8.
The following facts were considered :
a.) The velocity change during the crash test of the single post support was extremely low.
b.) Conventional dual post omni-directional slip bases have been tested with successful results, even when using more massive supports and sign panels.
c.) The mass of the dual and triple post supports for which you requested acceptance is no greater than the mass of the triple post support using the SB8 base.
In light of these facts the FHWA concurs in your request. Therefore the devices described above and shown in the enclosed drawings for reference are acceptable for use as Test Level 3 devices on the NHS under the range of conditions tested, when proposed by a State.
Please note the following standard provisions which apply to FHWA letters of acceptance:
Michael L. Halladay.
Acting Program Manager, Safety