Skip to contentSkip to contentUnited States Department of Transportation - Federal Highway Administration FHWA HomeFeedback

DOT logo
U.S. Department of Transportation

Federal Highway Administration

1200 New Jersey Avenue, SE.
Washington, DC 20590

September 17, 2008

In Reply Refer To: HSSD/CC-88B

Mr. John C. Durkos
V.P. Technical Support and Marketing
Road Systems, Inc.
3616 Howard County Airport
Big Spring, TX 79720

Dear Mr. Durkos:

This letter is in response to your request for 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.”


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.


The SKT and FLEAT have been successfully crash tested and accepted by the FHWA, most recently in FHWA Acceptance Letters CC-88, dated March 8, 2005, and CC-88A, dated June 1, 2008. The use of one anchor post, seven additional breakaway posts and subsequent transition to standard line posts were the same in these two w-beam guardrail terminals. Recent full scale crash tests have demonstrated that an 820C vehicle can safely ride down full strength W6x9 steel line posts. Your present request is to replace the last six breakaway posts in these terminals with these standard W6x9 line posts.

Crash Testing

In order to evaluate the safety performance of these new designs, three full-scale crash tests were conducted on the revised FLEAT terminal design. NCHRP recommends a total of up to 7 full-scale crash tests for gating guardrail terminals. We concur that only 3 of these tests are 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°. Because this test may allow the small car to strike a full strength line post, it is necessary for verification of the safety performance of the new terminals. Previous testing has shown that the small car engages more guardrail posts during tests of the FLEAT than during tests of the SKT. Hence, this test should be conducted on the FLEAT terminal in order to maximize the risk of failure.

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 results of test 3-30 will 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. The only thing that changed upstream of post #3 from the system that was approved previously is upper post #1. However, the behavior of this post will be more thoroughly explored in test 3-30 than in test 3-32. 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 3-31 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°. Because the vehicle can snag on posts 3 and 4 during this impact the new terminals need to be evaluated under this test condition. The flare of the FLEAT terminal effectively increases the impact angle for this test by approximately 6°. This test should be conducted. The increased effective impact angle makes testing of the FLEAT terminal more critical than a test of the SKT.

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. The flare on the end of the FLEAT produces a more critical impact and this test should also be conducted on this terminal.

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.

The test data summary sheets for the three recommended crash tests, FLT2P-1 (Test 3-35), FLT2P-2 (Test 3-34), and FLT2P-3 (Test 3-30) are enclosed for reference. In test FLT2P-3 there was a small hole in the floor pan caused when the nearly-stopped vehicle came to rest on the end of a guardrail post that was under the vehicle. We concur that this does not pose a significant risk to vehicle occupants. Otherwise, all occupant risk parameters of NCHRP Report 350 were within recommended guidelines. We concur that this testing shows acceptable performance for both FLEAT and SKT terminals when modified as described.


The modified FLEAT and SKT terminals 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
Director, Office of Safety Design
Office of Safety


Safety Home | FHWA Home | Feedback