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U.S. Department of Transportation

Federal Highway Administration

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

April 1, 2004

Refer to: HSSD/SS-123 Amendment #1

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

Dear Mr. Anderson :

Thank you for your correspondence requesting Federal Highway Administration (FHWA) acceptance of your company's 2 ¼ inch and 2 ½ inch SNAP'n SAFE ™ breakaway system for square sign supports for use on the National Highway System (NHS). Accompanying your letter was a report from the Texas Transportation Institute. You requested that we find these devices 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 the supports 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., Break-Away device 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 gray iron, class 35. The coupler is notched on each corner to an approximate depth of an eighth of an inch. This letter deals with both 2 ¼ inch and 2 ½ inch couplers designed for perforated square steel posts.

One sign support using the 2 ½ inch coupler was crash tested. For the test DES P7, the coupler was installed approximately 3 inches above grade and was anchored inside a 3 foot long, 3 inch by 3 inch perforated tube embedded in NCHRP Report 350 Soft Soil. The coupler was used to

support a 10 foot long 2 ½ inch by 2 ½ inch perforated steel tube post. One 3 feet by 3 feet square sign panel was attached to the perforated steel tube post approximately 7 feet above grade.

Test #




Occup. Speed

Delta V

400001-DES P7

34.8 km/hr

2.5 inch top



0.7 m/s

Occup. Speed: Occupant Impact Speed: 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. We agree in the assumption that the smaller 2 ¼ inch coupler would perform identically to the larger 2 ½ inch coupler. The results of testing met the FHWA requirements and, therefore, the SNAP'n SAFE ™ devices 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,

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


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