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U.S. Department of Transportation

Federal Highway Administration

1200 New Jersey Ave. S.E.
Washington, D.C. 20590

August 23, 2007

In Reply Refer To: HSSD/SS-152

Mr. Raymond Kisiel
Northwest Pipe Company
6307 Toledo Street
P.O. Box 2002
Houston, TX 77252-2002

Dear Mr. Kisiel:

Thank you for your letter of June 1, 2007, requesting the Federal Highway Administration’s (FHWA) acceptance of your company’s 30 inch anchors used with perforated square steel tube (PSST) posts as crashworthy sign supports for use on the National Highway System (NHS). Accompanying your letter was a report from the Texas Transportation Institute of the crash tests conducted. You requested that we find your company’s PSST sign 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.”

Introduction
Testing of the 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.

Testing
Bogie pendulum testing was recently conducted on your company’s various anchor lengths for PSST supports, ranging in length from 30 inches to 56 inches. The mass of the bogie pendulum was 820 kg. The tests were conducted at the typical 18 inch bumper height for small cars. Although pendulum tests are not routinely accepted for use with base bending or yielding supports, the crash behavior and post impact vehicle trajectory is fairly well known for PSST supports. Of the five tests conducted, the defining test was conducted on a 2-1/4 inch, 12 gauge PSST post inserted into a 2-1/2 inch by 30 inch, 12 gauge PSST anchor embedded 28 inches into standard soil. The summary of results from this test is enclosed. The post was inserted one foot into the anchor and secured in place with one 5/16 inch corner bolt and nut. A 48 by 36 inch by 5/8 inch thick plywood sign panel was attached to the post at a height of 7 feet from ground level. Detailed drawings of the sign support assembly are enclosed.

Findings
The pendulum bogie, traveling at a speed of 21.5 mph (35 km/hr), impacted the sign support at 18 inches above ground level. Upon impact, the support yielded at the impact point, pulled out of the ground, and came to rest 63 feet downstream of the impact point. The total crush to the pendulum nose (surrogate bumper) was 3.6 inches. The pendulum bogie test impact displayed a low potential for intrusion into the occupant compartment, measured a maximum acceleration of -0.6 g’s, and a velocity change of -2.9 m/s. The measured velocity and acceleration changes were well within acceptable limits, and because the support pulled out of the ground there was no remaining stub to measure. The results of testing met the FHWA requirements and, therefore, the device 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.

Additionally, you requested this PSST system to be considered acceptable for the following configurations:

The additional requests listed above are acceptable based on the test conducted on the 2-1/4 inch 12 gauge PSST post inserted into a 2-1/2 inch by 30 inch, 12 gauge PSST anchor embedded 28 inches into standard soil. The additional configurations requested are slightly less rigid systems and are likely to yield in the same manner while producing similar or less severe impact results. This acceptance is based on the reported crash performance of your device and is not meant to address the limitations of testing or the systems’ installation, maintenance, or repair characteristics.

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

Sincerely yours,

George E. Rice

George E. Rice, Jr.
Acting Director, Office of Safety Design
Office of Safety

Enclosures


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