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U.S. Department of Transportation

Federal Highway Administration

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

April 13, 2006

Refer to: HSA-10/SS-133

Mr. Gerald Okihara, P.E.
Traffic Design Engineer
City of Spokane
808 West Spokane Falls Blvd
Spokane, Washington 99201-3343

Dear Mr. Okihara :

Thank you for your E-mail correspondence of December 14, 2005, requesting the Federal Highway Administration (FHWA) acceptance of generic 2-inch and 2.5-inch schedule 40 pipes with pipe couplers as breakaway sign support systems for use on the National Highway System (NHS). You referenced the August 1989 test report from the Texas Transportation Institute (TTI) titled "Generic Small Sign Support System and Validation of Acceptable Support Performance". You requested that we find those supports 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." On April 6, 2006, TTI sent us the attached PDF scans of the Texas standard drawings as the best information they had available. We will take this opportunity to formally accept all the generic supports that were successfully tested under the referenced TTI study.

Testing of the supports was in compliance with the guidelines contained in the NCHRP Report 350 and Report 230, . 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. As the test and evaluation criteria for breakaway supports did not change materially from Report 230 using the 1800-pound car to Report 350, the results remain valid.

A brief description of the tested sign supports follows:

  1. Two U-Channel supports with bolted lap splice at ground level

    This installation consisted of a 6 ft wide by 5 ft tall plywood sign panel mounted on two Franklin steel four-pound-per-foot supports. These supports were attached to two 40-inch long stubs driven into "strong" soil at 36 inches on center. The supports were attached to the stubs in a 3.0-inch nested splice (stubs in front of the supports) with ½ inch spacers and 5/16 inch Grade 9 bolts, nuts, and washers. The bottom of the sign was mounted at 5 feet.

  2. Pipe supports with threaded coupler at ground level

    This installation consisted of a 4 ft wide by 5-foot tall plywood sign panel mounted with three cast u-bolts to a single 2 ½ inch schedule 40 steel pipe T-top support. A 2 ½ inch x 24 inch steel pipe was embedded in an 18-inch diameter x 30 inch deep concrete footing in strong soil. The top of the stub pipe and bottom of the signpost were threaded. The sign support was then attached to the footing using a pipe collar coupling.

  3. Pipe Post on multi-directional (triangular) slip bases

    The sign installation consisted of a U-frame constructed of 2-inch diameter steel pipe welded to a 3-inch diameter steel pipe support. The U-frame dimensions were 9 ft 1.5 inches on one side and 4 ft 6 inches on the other. The spacing between the U-frame uprights was 2 ft 8.5 inches. The 3-inch schedule 40 pipe support was 4 ft 10 inches long and equipped with a triangular slip base. A 3 inch x 36 inch steel pipe with triangular sip base and lifting ramp (FHWA note: this lifting ramp should be omitted) was embedded in a concrete footing 18 inches in diameter x 42 inches long. The concrete footing was placed in "strong" soil. The sign base was attached to a footing using 5/8 inch x 2 ½ inch high strength hex bolts, washers, and nuts. All signs were attached using 2 cast pipe clamps per sign with u-bolts. The lowest sign was mounted at 5 ft from the ground.


Full-scale automobile testing was conducted on these generic sign supports devices, all of which were founded in "strong" soil. The complete devices as tested are shown in the Enclosures.

Test #


Vehicle Mass



Delta V.


18.9 mph

816 kg

Dual Franklin 4 ppf posts

3.1 m/s

3.2 m/s


60.5 mph

816 kg

Dual Franklin 4 ppf posts


2.4 m/s


20.6 mph

816 kg

2.5" Pipe coupler in concrete

4.6 m/s

4.9 m/s


60.7 mph

816 kg

2.5" Pipe coupler in concrete


3.0 m/s


19.7 mph

816 kg

Triangular slip base


1.8 m/s


59.8 mph

816 kg

Triangular slip base


2.5 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.

Damage was limited to bumper, hood, and roof damage. No direct windshield contact was observed in any of the above tests. Velocity changes were all within acceptable limits. The
U-channel stubs, and the 3-bolt slip base were both designed and installed with stub heights no greater than 4 inches. The 2.5-inch pipe stub was installed with the threaded coupler flush with the ground surface.

  1. Two 4 pound-per-foot, 60 ksi U-Channel supports with bolted lap splice at ground level
    Note that single post installations may be used.
    Note that 80-ksi steel U-channels may be used.
    Note that 3 pound per foot and lighter posts may be used.

  2. 2.5 inch diameter schedule 40 pipe supports with threaded coupler at ground level
    Note that 2.0-inch diameter schedule 40 pipe supports and bases may be used.

  3. 3-inch diameter schedule 40 pipe post on multi-directional (triangular) slip base
    Note that the riser should be omitted from triangular slip base designs as testing of other triangular slip bases showed it to be an impediment to proper operation.

The results of testing met the FHWA requirements and, therefore, the 3 breakaway 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 or municipality.

Please note the following standard provisions that apply to the FHWA letters of acceptance:

Sincerely yours,

/original signed by George E. Rice, Jr./


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


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