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U.S. Department of Transportation

Federal Highway Administration

400 Seventh St., S.W.
Washington, D.C. 20590

March 16, 2007

Refer to: HSSD/SS-146

Mr. Jim Anderson
Designovations, Inc.
339 Wildwood Road
Stillman Valley, IL 61084

Dear Mr. Anderson:

Thank you for your correspondence requesting Federal Highway Administration (FHWA) acceptance of your company's SNAP'n SAFE ™ round coupler breakaway system for sign supports for use on the National Highway System (NHS). Accompanying your request was a report from the Texas Transportation Institute. You requested that we find this device acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."

Testing of your device was in compliance 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' Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals.

The Designovations, Inc., round coupler is a cast iron frangible coupling connecting a ground stub and the sign post. The coupler fractures upon impact at a predetermined scored line in the coupling, releasing the sign post from the ground stub. The coupler, shown in the attached drawing for reference, is fabricated of ASTM A48 Grey Iron, Class 35. The coupler is notched on each corner to an approximate depth of an eighth of an inch. This letter deals with SNAP'n SAFE ™ round couplers designed for 2 3/8 inch diameter thin wall (16 Gauge) and other wall thicknesses up to and including schedule 40 (8 Gauge) round steel posts.

One sign support using the round coupler was crash tested and the summary of test results is enclosed. For the test DES P8, the coupler was installed approximately 3 inches above grade and was anchored inside a 3 foot long, 2 3/8 inch diameter steel tube embedded in the NCHRP

Report 350 Soft Soil. The coupler was used to support the 10 feet long, 2 3/8 inch diameter thin wall steel post. One 3 feet by 3 feet square sign panel was attached to the steel post approximately 7 feet above grade.

Test #





Delta V

400001-DES P8

34.5 km/hr

2.375 inch diameter

Steel Tube


0.1 m/s

Occupant Impact Speed (OIS): Speed at which a theoretical front seat occupant will contact the windshield (in meters per second).
Delta V: Speed change of the test vehicle (in meters per second).

Results of the test show the stub moved through the weak soil and deformed below the ground line, but the coupler still sheared as designed. Velocity change and deceleration are both within acceptable limits. There was no appreciable remains of the coupler left to protrude above the top of the stub, which had been installed such that the top of the stub would be at a height less than 4 inches above the ground. The results of testing met the FHWA requirements and, therefore, the thin wall (16 Gauge) and other wall thicknesses up to and including schedule 40 (8 Gauge) round steel sign supports utilizing your SNAP'n SAFE ™ round coupler as described above and shown in the enclosed drawing 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 that apply to the FHWA letters of acceptance:

Sincerely yours,

/original signed by /

John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety


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