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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-111

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U.S. Department of Transportation
Federal Highway Administration

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

December 22, 2010

In Reply Refer To: HSSI/CC-111

Dean L. Sicking, Ph.D., P.E.
Director
Midwest Roadside Safety Facility
130 Whittier Bldg.
220 Vine Street
Lincoln, NE 68583-0583

Dear Dr. Sicking:

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

Name of device: Low Tension Cable Guardrail End Terminal
Type of device: End Terminal
Test Level: NCHRP Report 350 Test Level 3 (TL-3)
Testing conducted by: Roadside Safety Facility (MwRSF)
System Designator: SEC10
Date of request: August 1, 2010

You requested that we find this device acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 testing guidelines.

Requirements
Roadside safety devices should meet the guidelines contained in the NCHRP Report 350. The FHWA memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 24, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
Per the submitted crash test report, the Low Tension Cable Guardrail End Terminal system is designed for low tension cable guardrail systems. The total length of the installation was 254 feet and consisted of four major structural components: (1) Wire ropes; (2) posts; (3) cable compensator assemblies, and (4) anchor assemblies. The design details of this system are included as an enclosure to this correspondence. Three 3/4-inch diameter cables comprised of 3 x 7 wire rope used for the rail elements. The cable rails were supported by nineteen posts with an upper cable mounting height of 30 inches, a middle mounting height of 27 inches, and a lower mounting height of 24 inches. The cables were tightened through the use of cable compensators. The ends of the cables were threaded rods that terminated in the cable anchor. The threaded rods were attached to the cable anchor by three 2-inch diameter galvanized washers and two 3/4-inch diameter galvanized Grade 5 heavy hex nuts. The anchor bracket posts, post number 1 and 19, were 96-inch long W6 x 25 sections with a 24-inch x 24-inch soil plate welded along the downstream flange of the post. The anchor post was embedded to a depth of 96-inches. A 141/2-inch x 9-inch x 1/2–inch plate was welded to the top of the anchor post to which the cable anchor bracket was bolted with four 2/4-in x 2-1/2-inch Grade 5 hex head bolts. Post Numbers 2 and 18 were configured with S3 x 5.7 sections measuring 30 inches long for the slip post and W6 x 9 sections measuring 72 inches long for the foundation posts. The foundation post was embedded to a depth of 70 inches. A slip base plate was welded to the bottom of the skip post and the top of the foundation post. Four 1/2-inch x 2-inch ASTM A307 bolts with nuts and washers were used to form the slip base configuration. Post Numbers 3 through 7 were configured with S3 x 5.7 sections measuring 30 inches long for the slip post and W6 x 9 sections measuring 72 inches long for the foundation posts. The foundation post was embedded to a depth of 70 inches. A slip base plate was welded to the bottom of the slip post and the top of the foundation post. Four 1/2-inches x 2-inch ASTM A307 bolts with nuts and washers were used to form the slip base configuration. The line posts, post numbers 8 through 17, consisted of 63-inch long S3 x 5.7 sections, with 30-inch embedment depth and a 8-inch x 24-inch x 1/4-inch soil plate welded along the back flange of the post. These line posts were spaced 16-ft. on center with a soil plate embedment depth of 30 inches. The top cable hook was located 3-1/2 inches down from the top of the post with the middle and lower cable hooks 6½-inches and 9-1/2-inches for the top of the post, respectively.

A steel cable anchor bracket was bolted to the top base plate of the steel anchor post. The steel cable anchor bracket was modified from existing designs in order to accept a new, fabricated steel cable release lever device. The cable release lever consisted of a pair of 17-inch long 1-1/4-inch x 1-1/4-inch x 3/16-inch vertical tubes mounted 2 inches apart on a 9-inch x 3-inch x 1/2-inch steel plate. The cable release lever was implemented in order to dislodge and release the wire rope cables during end-on vehicular impacts with the end terminal system. The steel cable anchor bracket was designed to accept the ends of the three 3/4-in. diameter by 3 x 7 wire rope cables. A 0.375-inch diameter, 32-inch long 7 x 19 galvanized aircraft cable was added to retain the cable release lever to the anchor bracket upon impact.

Crash Testing
Per the submitted crash test report, the following physical crash testing was conducted:

  1. Test 3-30 (820C/ 100km/hr. / 0 degrees with 1/4-point offset).
  2. Test 3-35 (2000P/ 100 km/hr. / 20 degrees).

In addition, the following tests are requested to be waived per the following comparisons:

Test Number Test Level Requested Comparison
3-31 TL-3 Not necessary since Test 3-30 is considered worst case.
3-32 TL-3 Not necessary since Test 3-30 is considered worst case; and similar to prior successful Crash Test No. 104 on New York Department of Transportation (NYDOT) terminal design.
3-33 TL-3 Not necessary since Test 3-30 is considered worst case.
3-34 TL-3 Not necessary due to equivalence to a prior successful crash testing of similar NYDOT terminal design tested at 20 degrees.
3-39 TL-3 Not necessary due to equivalence to prior successful crash testing of two small car tests (Tests No. 98 and 404211-6) performed on the reverse direction of similar NYDOT design.

Findings
The FHWA concurs to the submitted physical crash testing and to requested comparisons relating to the proposed TL-3 Low Tension Cable Guardrail End Terminal. Therefore, the TL-3 Low Tension Cable Guardrail End Terminal System meets the TL-3 impact conditions and evaluation criteria for a NCHRP 350 Terminals, and is acceptable for use on the NHS when requested by a highway agency.

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

 

Sincerely yours,

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

2 Enclosures

Page last modified on January 17, 2013.
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