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U.S. Department of Transportation

Federal Highway Administration

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

February 9, 2006

Refer to: HSA-10/SS-132

Mr. Mark T. Salman, President
Sign Support Systems
P.O. Box 8041
Greensboro, NC 27419

Dear Mr. Salman :

Thank you for your letter of November 28, 2005, requesting Federal Highway Administration (FHWA) acceptance of a new model of your company’s Break Out Coupler for perforated square steel tubes as a breakaway sign support system 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 new Break-Out Coupler 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' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.

The Break-Out Coupler is a cast-iron (ASTM A536 65-45-12 alloy) coupling with a shear section machined to a pre-set diameter to ensure breakaway performance of up to a maximum of 90 percent of the yield strength of the post it is used with. It was originally found acceptable in our letter SS-98 dated August 29, 2001, with U-channel posts and 2-inch perforated square steel tube (PSST) sign supports. The new version you have recently tested is designed for
2 ½ inch PSST supports. The cast neck of this model is subsequently machined with a groove that yields a final diameter of 1.900 inches.

The sign support was 2 ½ inch x 2 ½ inch North West Pipe PSST with 12 gage fins (soil anchor). The 48x48x5/8 inch plywood sign panel was attached using 3/8 inch x 4-inch bolts 6 inches from the top and bottom of the sign panel. The two-piece Break-Out casting was held together with 1/2 inch x 3 inch grade 8 flange bolt. The PSST support was secured into the Break Out casting with two 5/16 x 4 inch grade 5 hex-head bolts.

Pendulum bogie testing was conducted on your company’s devices. The mass of the bogie test vehicle was 839 kg in all tests. Two similar tests were run in the NCHRP Report 350 Standard Soil to verify the consistent performance of the Break Out Coupler. Both tests included the installation of a soil anchor just below the surface. A plywood sign panel was mounted to the impact face of the PSST at a height of 7 feet to the bottom. The complete devices as tested are shown in the enclosures.

Test #


Impact Speed


Delta V

Est. 60 mph Delta V


Test 3-60

35.0 km/hr

Soil Plate

1.8 m/s

0.7 m/s


Test 3-60

35.1 km/hr

Soil plate

1.5 m/s

0.7 m/s

Occupant Impact Speed: Speed at which a theoretical front seat occupant will contact the windshield. In these two tests the device did not slow the vehicle enough to result in an occupant impact, i.e. “no contact.”
Delta V: Speed change of the test vehicle. In meters per second.
Est. 60 mph Delta V: Delta V of a theoretical high-speed test estimated using data from the pendulum test.

Velocity changes were all within acceptable limits, and the only stub remaining was flush with the level of the surrounding soil. The anchor moved 1.1 inches in the soil during test SKD-P1 and moved 0.24 inches during test SKD-P2. The results of testing met the 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 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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