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Safety Eligibility Letter CC-103a

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U.S. Department of Transportation
Federal Highway Administration

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

August 16, 2011

In Reply Refer To: HSSD/CC-103A

Mr. Gerrit A. Dyke, P.E.
Vice President of Engineering and R & D
Barrier Systems, Inc.
3333 Vaca Valley Parkway, Suite 800
Vacaville, CA 95688

Dear Mr. Dyke:

This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of a modified trailer-mounted attenuator for use on the National Highway System (NHS).

Name of system: U-MAD Trailer-Mounted TMA
Type of system: Trailer-Mounted Attenuator
Test Level: NCHRP Report 350 TL-3
Testing conducted by: not applicable
Date of request: December 30, 2010
Date received by FHWA January 7, 2011

You requested that we find a modified version of your previously-accepted U-MAD trailer attenuator 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 devices should meet the guidelines contained in NCHRP Report 350 if tested prior to January 1, 2011, and the guidelines in AASHTO's Manual for Assessing Safety Hardware if tested after that date.  The FHWA memorandum "ACTION: Identifying Acceptable Highway Safety Features" of July 24, 1997, provides further guidance on crash testing requirements of longitudinal barriers and crash cushions.  Modifications to previously-accepted devices that are not likely to affect crash performance may be accepted without additional crash testing.

The U-MAD trailer-mounted TMA was previously accepted as a TL-2/TL-3 design in FHWA acceptance letter CC-103.  This design was modified by the addition of mounting brackets and a removable sign board assembly, as described below.  Based on the results of your analysis, as summarized below, the FHWA agrees that your modified trailer-mounted attenuator remains a crashworthy design under NCHRP Report 350 at TL-2 and TL-3, depending on which energy-absorbing cartridge is mounted on the trailer.

The basic U-MAD trailer-mounted attenuator described in detail in FHWA acceptance letter CC-103 was modified to add mounting brackets for a removable illuminated sign board assembly. Modifications to the trailer frame consist of two upright steel tubes and gussets welded to the trailer frame.  The uprights are 3.5-inch × 2.5-inch × 3/16-inch (90-millimeter × 65-millimeter × 5-millimeter) steel tubes and the gussets are 1.5-inch × 1.5-inch × 3/16-inch (40-millimeter × 40-millimeter × 5-millimeter) steel angles.  The sign support frame is made from 2-inch × 3-inch × 3/16-inch (50-millimeter × 75-millimeter × 5-millimeter) steel structural tubing designed to accommodate a 4-foot × 8-foot (1.2-meter × 2.4-meter) sign board.  Enclosure 1 shows the modified trailer and Enclosure 2 shows the trailer with a TL-3 U-MAD cartridge and a sign board in place.

The design of the U-MAD trailer-mounted attenuator is such that an impacting vehicle is not likely to contact the trailer assembly when it is loaded with a TL-2 or a TL-3 U-MAD cartridge. The weight of the sign board and mounting hardware increases the total weight of the unit by appro×imately 12 percent.  Your conservation of momentum analysis concluded that this minor increase in weight would not cause a significant increase in the occupant impact velocity reported in test 3-51 for the un-modified design.  Your structural analysis further concluded that the sign board mounting structure and hardware is sufficient to withstand the ma×imum loads associated with an NCHRP Report 350 TL-3 impact.  We have reviewed your analysis and agree with your conclusions.

Based on the considerations noted above, the FHWA agrees that the U-MAD trailer-mounted attenuator, as modified, remains acceptable as an NCHRP Report 350 TL-2 or TL-3 attenuator.
Please note also that the following provisions apply to FHWA letters of acceptance:


Sincerely yours,

/* Signature of Michael S. Griffith */
Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety


Page last modified on January 17, 2013.
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