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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-88D

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U.S. Department of Transportation
Federal Highway Administration

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

January 29, 2010

In Reply Refer To:
HSSD/CC-88D

Mr. John C. Durkos
Vice President 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 the Federal Highway Administration’s (FHWA) acceptance of two modified roadside safety devices for use on the National Highway System (NHS).

Name of devices: TL-2 SKT and TL-2 FLEAT W-Beam Guardrail Terminals for the Midwest Guardrail System (MGS)
Type of device: Midwest W-Beam Guardrail Terminals
Test Level: NCHRP Report 350 Test Level 2
Testing conducted by: N/A
Date of request: May 29, 2009
Date acknowledged: June 29, 2009

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 or the American Association of State Highway and Transportation Officials’ “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 Sequential Kinking Terminal (SKT) and Flared Energy Absorbing Terminal (FLEAT) have been successfully crash tested and accepted by the FHWA:

Test Level 3 (TL-3) SKT and FLEAT terminals for the MGS are covered by the FHWA Acceptance Letters CC-88 dated March 8, 2005, and CC-88A dated June 1, 2008.

Test Level 2 (TL-2) SKT and FLEAT terminals for the standard metric height guardrail system are covered by the FHWA Acceptance Letters CC-46B dated May 21, 1999, for the TL-2 FLEAT terminal and CC-40A dated February 4, 2000, for the SKT terminal.

Enclosed for reference are drawings of your proposed TL-2 MGS SKT and TL-2 FLEAT steel post and wood post terminals. The designs of these TL-2 MGS terminals are essentially the same as the Accepted TL-3 MGS terminals except for the terminal length and number of breakaway posts. For the TL-2 SKT-MGS terminal, the length is reduced from 50 feet, 0 inches to 25 feet, 0 inches with fewer breakaway posts, i.e., for the TL-2 system, post #6 and beyond are now a standard line post. For the TL-2 FLEAT-MGS terminal the length of the straight flare is reduced from 37 feet, 6 inches to 25 feet, zero inches. The corresponding range of end-offset is reduced from 2 feet, 6 inches and 4 feet, 0 inches to 1 foot, 8 inches and 2 feet, 8 inches respectively. The TL-2 FLEAT-MGS terminal also has one fewer breakaway post, i.e., for the TL-2 system, post #6 is now a standard line post. Also, note that the layouts of the TL-2 MGS terminals are identical to those used for the approved TL-2 metric height terminals.

Analysis
NCHRP Report 350 guidelines recommend a total of up to seven full-scale crash tests for gating guardrail terminals. It was your opinion that no additional full-scale crash tests are required to evaluate the safety performance of these proposed TL-2 MGS terminal designs. First, the layouts of the TL-2 MGS terminals are the same as those for the FHWA-accepted TL-2 metric height terminals. This tells us that the proposed TL-2 MGS terminals will also be able to manage the energy of the impacting vehicle as did the crash-tested systems. Second, the TL-2 MGS terminal designs are essentially the same as those of the approved TL-3 MGS terminal designs except for the shorter terminal length and fewer breakaway posts.

Findings
The modified TL-2 FLEAT-MGS and TL-2 SKT-MGS 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

Enclosures

Page last modified on January 17, 2013.
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