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Safety Eligibility Letter B-192

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U.S. Department of Transportation
Federal Highway Administration

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

May 29, 2009

In Reply Refer To:

Mr. Robert Williams
President, BWW Enterprises, Inc.
5733 South Dale Mabry Highway
Tampa, FL 33611

Dear Mr. Williams:

This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of a roadside safety product for use on the National Highway System (NHS).

Name of system:BWW Enterprises Diamond Block
Type of system:W-Beam Guardrail Offset Block, 8-inch
Test Level:NCHRP Report 350 TL-3
Testing conducted by:Midwest Roadside Safety Facility
Date of request:March 4, 2009

You requested that we find this product 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.”

Roadside safety systems should meet the guidelines contained in the NCHRP Report 350. The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

The Diamond Block is comprised of approximately 97.65 percent recycled high density polyethylene plastic, 1.25 percent chemical blowing agent, 1 percent carbon black, and 0.1 percent UV stabilizer. It measures approximately 7.5 inches x 4.6 inches x 14.5 inches tall with a recess on the back to accommodate the face of the guardrail post. The voided design of the block is seen in the drawing which is enclosed for reference. The block’s weight is in the range of 5.8 to 5.9 pounds.

Crash Testing
The Midwest Roadside Safety Facility conducted two bogie vehicle tests using standard steel guardrail posts held rigidly in a test foundation. One test evaluated the performance of a standard routed wood blockout, and the other evaluated the Diamond Block (named EXUL-1 during the testing phase). In both cases the bogie vehicle impacted a short length of w-beam rail mounted on the face of the blockout. In the wood blockout test the 2190-pound bogie impacted the test article at 20 mph. In the test of the Diamond block the 1817-pound bogie impacted the test article at 23.0 mph.

Based on the results of the crash tests, no significant differences were observed between the performance of the wood and plastic spacer blocks. Both blocks displayed similar levels of permanent damage after impact. Analysis of the high-speed video showed that the plastic block remained firmly attached to the post during the impact with the router gripping the front flange of the post until it was overridden by the bogie vehicle. No concerns were observed with regards to the dynamic performance nor the structural integrity of the plastic blockout when compared with the wood. In addition, the force vs. deflection curve for the Diamond Block test was cross plotted against component testing using results from two previously FHWA accepted plastic blockouts. The results of this comparison showed that the Diamond blockout displayed similar force vs. deflection behavior to previously accepted designs.

Therefore, the guardrail offset block described above and detailed in the enclosed drawing is acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency.

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


Sincerely yours,

Signature of David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety


Page last modified on June 24, 2011.
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