April 1, 2004
Refer to: HSA-10/SS-120
Mr. Jim Anderson
339 Wildwood Road
Stillman Valley, Illinois 61084
Dear Mr. Anderson:
Thank you for your letter of February 12, 2003, requesting Federal Highway Administration (FHWA) acceptance of your company’s 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 and videos of the crash tests. You requested that we find the Designovations, Inc., frangible cast iron Break-Away device acceptable for use on the National Highway System 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' (AASHTO) 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 has a score 1/32 inch deep by 1/32 inch wide around its perimeter. This letter deals with the larger coupler designed for a 2 inch perforated square steel post.
Bogie pendulum testing was conducted on your company’s devices. The mass of the pendulum bogie was 820 kg in all tests, and it was affixed with a crushable honeycomb nose simulating the crush characteristics of a small car.
Two versions of a sign support using the coupler were crash tested. The first, test DES P1, used a 2 inch UniStrut perforated square steel tube sign post with a 2.25 inch UniStrut ground stub inserted in weak soil. The top portion of the coupler measured 1.75 inches on a side. The second test, DES P2, the stub conditions were the same, but the coupler supported a 2.0 inch fiberglass composite post with a 0.25 inch wall thickness. The top of the coupler in the second test measured 1.50 inches on a side. In both tests, a 36-inch octagonal aluminum sign panel was bolted at a mounting height of 84.5 inches.
|Test #||Speed||Version||Article||Occup. Speed||Delta V|
|1 400001-DES P1||35.0 km/hr||1.75 inch top||PSST||None||1.67 m/s|
|2 400001-DES P2||35.2 km/hr||1.50 inch top||Fiberglass||None||0.64 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.
In both tests the stubs moved through the weak soil and deformed below the ground line, but the coupler still sheared as designed. Velocity changes and decelerations were all within acceptable limits. There were 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 SNAP’n SAFE ™ 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 that apply to the FHWA letters of acceptance:
/Original Signed By Harry Taylor/
for: John R. Baxter, P.E.