U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content
FacebookYouTubeTwitterFlickrLinkedIn

Safety

eSubscribe
eSubscribe Envelope

FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter - CC-12Q

Download Version
PDF [88 KB]

DOT logo
U.S. Department of Transportation
Federal Highway Administration

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

March 15, 2010

In Reply Refer to: HSSD/CC-12Q

Mr. Steve Brown
President
Trinity Highway Products, LLC
2525 N. Stemmons Freeway
Dallas, TX 75207

Dear Mr. Brown:

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

You requested that we find these devices 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 FHWA Memorandum “Action: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
The ET-Plus and ET-Plus 31 have been successfully crash tested and accepted by the FHWA, most recently in FHWA Acceptance CC-12J, dated June 24, 2002, CC-12L, dated April 11, 2003, and CC-94, dated September 2, 2005. The use of one anchor post and subsequent transition to standard line posts were the same in these two w-beam guardrail terminals. The obvious difference is the use of seven additional breakaway posts and the 27 5/8-inch rail height in the ET-Plus and five additional breakaway posts and 31-inch rail height in the ET-Plus 31. Recent full scale crash tests have demonstrated that an 820C vehicle can safely ride down full strength W6x8.5 steel line posts that are not rigidly connected to the w-beam rail. Your present request is to replace the last six breakaway posts in ET-Plus and the last 4 breakaway posts in the ET-31with these standard W6x8.5 line posts.

Crash Testing
In the safety performance evaluation of these new designs, full-scale crash tests were not conducted on either revised design. NCHRP recommends a total of up to 7 full-scale crash tests for gating guardrail terminals. We concur that none of these tests is needed to verify the safety performance of the proposed new terminal designs, as summarized below.

Test 3-30 involves an 820C vehicle striking the end of the terminal at a speed of 100 km/hr with ¼ offset and an angle of 0°. Recent full scale crash tests have demonstrated that an 820C vehicle can safely ride down full strength W6x8.5 steel line posts. Hence, Test 3-31 is not necessary for evaluating the performance of the new terminal designs.

Test 3-31 involves a 2000P vehicle striking the end of the terminal at 100 km/h and 0°. Numerous full-scale crash tests have shown that the 2000P vehicle is capable of riding down full strength guardrail posts. Further, the previous results of test 3-30 provide a much better indication of the consequences of a vehicle striking an unmodified line post. Thus, Test 3-31 is not necessary for evaluating the performance of the new terminal designs.

Test 3-32 requires an 820C vehicle striking the end of the terminal at 100 km/h and an angle of 15°. Historically the third post in a tangent energy absorbing terminal has not been broken during this impact. Nothing was changed upstream of post #3 from the systems that were approved previously. Therefore, we concur there is no need to conduct this test.

Test 3-33 incorporates the same impact conditions as test 3-32 with a 2000P vehicle. This test is not necessary for the same reasons that Test 3-32 is not required.

Test 3-34 involves an 820C vehicle striking the terminal at its critical impact point at a speed of 100 km/h and an angle of 15°. Previous 3-34 testing was successfully conducted on ET-Plus (HSA-10/CC-12J) with W8x10 breakaway Steel Yielding Terminal Posts (SYTP)] at post locations 2 through 8. Also, this test was successfully conducted with another terminal at a greater impact angle than would be required with the ET-Plus and ET-31. Therefore, we concur there is no need to conduct this test.

Test 3-35 examines the safety performance of the terminal for impacts at the beginning of the length-of-need. This test involves a 2000P striking at the beginning of length-of-need. Previous 3-35 testing was successfully conducted on ET-Plus and ET-Plus 31 with breakaway posts (SYTP) at post locations 2 through 8 and 2 through 6 respectively. Therefore, 3-35 testing on the terminals with full strength W6x8.5 steel line posts at post location 3 and beyond is not required.

Test 3-39 involves a 2000P vehicle impacting the midpoint of the terminal in a reverse direction at a speed of 100 km/h and an angle of 20°. As mentioned above the 2000P test vehicle has been shown to be capable of riding down a full strength line post without posing serious threats to the occupants. Hence this test is also considered to be unnecessary.

In these tests we concur that the performance of the last six breakaway posts in the ET-Plus and the last 4 breakaway posts in the ET-31 terminals would not have been adversely affected by replacing the yielding posts with standard line posts.

Findings
The modified ET-Plus and ET-Plus 31 described above and detailed in the enclosed drawings are acceptable for use on the NHS under the range of conditions tested, when 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

Enclosures

Page last modified on January 17, 2013.
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000