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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-102A

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U.S. Department of Transportation
Federal Highway Administration

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

August 19, 2011

In Reply Refer To: HSST/CC-102A

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 Federal Highway Administration (FHWA) acceptance of a roadside safety system for use on the National Highway System (NHS).

Name of system: X-Tension Terminal at 31-inch (787-millimeter) height
Type of system: Tangent & Flared Re-directive W-Beam Terminal
Test Level: NCHRP Report 350 TL-3
Testing conducted by: Safe Technologies Inc.
Date of request: December 20, 2010
Request acknowledged: December 27, 2010
Task Force 13 designator: SEW19b Tangent
SEW20b Flared

You requested that we find this system 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."

Requirements
Roadside safety devices tested prior to January 1, 2011 should meet the guidelines contained in NCHRP Report 350; those tested after that date must follow the guidelines contained in the American Association of State Highway and Transportation Officials' (AASHTO) Manual for Assessing Safety Hardware (MASH).  The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997 provides further guidance on crash testing requirements for longitudinal barriers.

Decision
The following system design was found acceptable, with details provided below:

Description
The original X-Tension end terminal was tested and accepted for use on the NHS in FHWA Acceptance Letter CC-102 for tangent, flared, and median applications.  This earlier testing was done with the terminal set to match a guardrail height of 27 5/8 inches (702 millimeters).  This request is for acceptance of the X-Tension set at a height of 31 inches (787 millimeters) to match the guardrail when installed at the higher height.  The only changes made to the original X-Tension design were a reduction of the post embedment depths for posts #2 through #7 and the use of a longer Post #1 top section.  The general layout of the flared, tangent, and median X-Tension designs and a dimensioned drawing of the longer post are shown in Enclosures 1and 2, respectively.

Crash Testing
The required crash testing was developed in consultation with the FHWA's Office of Safety Design and one test was conducted to validate the crashworthiness of the modified design. NCHRP Report 350 Test 3-34 was run on the flared layout of the X-Tension Terminal. This test was selected to address the highest occupant risk condition where the potential for small vehicle underride and maximum vehicular contact with the strong posts of the X-Tension are maximized.  The cable anchor system extending from the impact head to the ground reduces the likelihood of the small car under riding the terminal in a head-on impact, and the increased height throughout the entire terminal can be expected to capture larger vehicles with little probability of override.

Test 3-34 with the 820C vehicle impacting the side of the system at the critical impact point (CIP) at a 15-degree angle was conducted using the flared X-Tension design at the 787-millimeter (31-inch) height.  The CIP was determined to be upstream from Post #2. Enclosure 3 is a summary of the crash conditions and results.

Findings
You requested FHWA acceptance of the X-Tension Terminal as an NCHRP Report 350 TL-3 Redirective W-Beam Terminal:

These options are 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 Michael S. Griffith */
Michael S. Griffith
Director, Office of Safety Technologies
Office of Safety

Enclosures

Page last modified on January 17, 2013.
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