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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-89A

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U.S. Department of Transportation
Federal Highway Administration

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

January 21, 2010

In Reply Refer To:
HSSD/CC-89A

Mr. Brian Smith
Trinity Highway Products, LLC
2525 N. Stemmons Freeway
Dallas, TX 75207

Dear Mr. Smith:

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

Name of device: 70 mph HEART
Type of device: Crash Cushion
Test Level (TL): NCHRP Report 350 TL-3
Testing conducted by: Texas Transportation Institute
Date of request: May 28, 2009
Date of completed package: October 28, 2009
Task Force 13 Designator: SCI21

You requested that we find this device acceptable for use on the NHS under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features.”

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

Description
The 70 mph Hybrid Energy Absorbing Reusable Terminal (HEART) attenuator consists of deformed (hinged) High Molecular Weight/High Density Polyethylene panels along each side connected to steel diaphragms mounted on tubular steel tracks. The assembled unit is approximately 28 feet, 9 inches long when a concrete barrier is used as the backup structure, 32 inches high in the front two-thirds and 34 inches high for the rear third, and 25 inches wide at the diaphragms with a maximum width of 39 inches between diaphragms 3 and 4. The front anchorage consists of a W8 x 13 upper release post mounted to a 1/2-inch thick base plate. There are two slots at the slip plane between the upper and lower post through which tensioning cables are anchored.

When the upper release post is impacted, the tensioned cables connected to diaphragm 2 are released and the side panels and steel diaphragms are pushed rearward along the base track. This track consists of a pair of 2-inch x 5-inch x 1/4-inch structural tubes stitch-welded above two C3 x 4.1 standard channels. The channels serve as spacers allowing the diaphragms to move longitudinally along the structural tubing during frontal impacts. Anchor bolts, 3/4-inch diameter x 7 1/2-inches long, are placed through the front anchorage base plate and anchor bolts, 3/4-inch diameter x 10-inches long, are placed through the structural tubing and channel at locations that can be accessed without removal of the plastic side panels or diaphragms and into 6-inch reinforced or 8-inch thick non-reinforced concrete, or anchor bolts, 5/8-inch x 18-inches long, are placed through the front anchorage base plate and structural tubing and channel and into 8-inch thick asphalt.

The rear backup structure can be either concrete barrier or an 8-inch x 12-inch x 1/2-inch structural tube welded to a 3/4-inch thick base plate. The last diaphragm is either bolted to brackets that are anchored to the concrete barrier or bolted to the structural tube. A second set of tensioning cables, attached to diaphragm 2, terminate on the rear side of diaphragm #12. The enclosed drawing shows the general layout of the unit and selected components.

Crash Testing
The original TL-3 HEART was crash tested and found acceptable in our FHWA Acceptance Letter CC-89 dated March 15, 2005. Your present request is for a modified version of the HEART (described above) that was crash tested at 70 mph in an NCHRP Report 350 Test 3-31 Modified. In this modified test the impact speed was established to be 70 mph instead of the 62.5 mph required by NCHRP Report 350. The test data summary sheet for that impact is enclosed for reference.

You noted that the longitudinal ridedown acceleration was 20.4 g. NCHRP Report 350 recommends a maximum 20 g (two significant digits) for this occupant risk factor. Because the recorded acceleration can be rounded down to 20 g, FHWA has accepted longitudinal ridedown acceleration up to 20.4 g in the past.

Findings
The tested unit met Report 350 evaluation criteria for a TL-3 crash cushion for the test 3-31 head-on impact with the 2000P truck at a nominal speed of 70 mph. The device is acceptable for use on the NHS as a TL-3 device when acceptable to a highway agency in uni-directional traffic flow applications as well as in bi-directional traffic flow applications provided the plastic side panels are lapped in the direction of traffic flow and an acceptable transition is used.

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

 

Sincerely yours,

Signature of David A. Nicol

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

Enclosures

Page last modified on January 17, 2013.
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