Federal Highway Administration
400 Seventh St., S.W.
Washington, D.C. 20590
March 21, 2007
In Reply Refer To: HSSD/B-156
Mr. Andrew Artar
Vice President Sales and Marketing
Gregory Industries, Inc.
4100 13th Street, SW
Canton, OH 44170
Dear Mr. Artar:
In your letter of December 13, 2006, you requested the Federal Highway Administration's (FHWA) acceptance of Single-Sided and Double Sided Thrie-Beam called the GMS-TB Guardrail System at the National Cooperative Highway Research Program (NCHRP) Report 350 test level 3 (TL-3). To support your request, your company sent a copy of the Southwest Research Institute report dated November 30, 2006, entitled "NCHRP Report 350 Test 4-11 Full-Scale Crash Evaluation of a Single-face GMS-TB Guardrail System" and digital videos of the crash test conducted on the GMS-TB Guardrail System. You also requested the waiver of tests 3-10 of the Single-Sided and Double Sided GMS-TB Guardrail System and test 3-11 of the Double-Sided GMS-TB Guardrail System.
Longitudinal barriers should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features.” The FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements.
The GMS-TB Guardrail System is a Thrie-Beam longitudinal barrier which uses 12-gage Thrie-Beams mounted directly on conventional W6 x 8.5 posts without blockouts or backup plates at any of the posts. The Thrie-Beams are attached to the posts with a single proprietary Mini Spacer (GMS) fastener at each post, with the fastener being attached to the Thrie-Beam at the lower flange of the Thrie-Beam (using a 0.64 m (25 in.) mounting height). All guardrail splices are located at posts. The guardrail panels are each 3.81 m (12.5 ft) long, the posts are spaced at 1.91 m (6.25 ft), and the height of the top of the guardrail is 0.99 m (39 in). This height constitutes an increase of approximately 100mm (4 in) compared to the conventional SGR09 (a,b,c) Thrie-Beam systems and accounts for higher centers of gravity of the current vehicle fleet. The ground clearance of the system is 483 mm (19 in), which is the same ground clearance that was used in the W-beam GMS designs previously accepted by the FHWA (acceptance letter HSA-10/B150). The proprietary GMS fastener is a critical element of the system. It ensures that Thrie-Beam panels disengage from the posts on impact and are not pulled down to the ground and rotated by the posts. Such performance lowers the probability of vehicles overriding the system. Also, posts disengaged from the guardrail have less of a snagging potential compared to posts attached to the guardrail. Design details for the proprietary GMS fastener are shown in Enclosure 1.
Test article installation
The test article’s length-of-need section was 45.72 m (150 ft) long. The 12 guardrail panels between the end anchors were each 3.81 m (12.5 ft) long, the posts were spaced at 1.91 m (6.25 ft), and the height of the top of the guardrail was 0.99 m (39 in). The barrier system was terminated at either end with modified Type T Anchors (Foundation Tube Option), without blockouts, and without struts between posts. This end anchor is designed to span three posts. However, rectangular washers were added at posts 1 through 4 and 28 through 31 for purposes of this length-of-need test only. Drawings of the test article are presented in Enclosure 1. Note that the end anchor systems were assembled as shown, except that Thrie-Beam rails were used in place of the W-Beam rails and the anchor cable bracket was attached to the lower flange of the Thrie-Beam rail.
Including the extended end anchors, the entire longitudinal barrier spanned 31 posts, with the length-of-need section mounted from post 4 through post 28. The total length of the longitudinal barrier in the test installation, including the end anchors, was 57.15 m (187.5 ft).
Full-scale crash testing to evaluate the impact performance of the GMS-TB Guardrail System included test 3-11. The results of this test are summarized in Enclosure 2. A comparison of the test results with the evaluation criteria set forth in the NCHRP Report 350 indicates compliance with all recommended criteria for the test performed.
The GMS-TB Guardrail System performed as intended. In the posts that were directly contacted by the test vehicle (Posts 13 through 19), the guardrail was released from the posts. In the vehicle contact region, all of the fasteners were sheared at the front face of the post during the impact of the vehicle with the guardrail and posts, except for Post 16 where the fastener was not sheared. All of these fasteners exhibited a uniform U-shaped deformation of the release washers. Outside of the vehicle contact region, the fasteners in Posts 20 through 24 released from the guardrail without being sheared, and in Post 25 the fastener released from the guardrail and was sheared at the front face of the post. These fasteners also exhibited a uniform U-shaped deformation of the release washers. None of the Thrie-Beams failed and all of the splice joints remained fastened together. The guardrail was not smashed flat at any of the posts in the impact region and for the most part maintained its Thrie-Beam shape.
Previously, you successfully conducted test 3-10 on a Double-Sided (median) GMS W-beam barrier (FHWA acceptance letter HSA-10/B-150). I agree that this previously conducted test is comparable to test 3-10 on either Single-Sided or Double Sided GMS-TB Guardrail Systems. It is critical that the ground clearance and mounting height of the GMS-TB Guardrail Systems are the same as those used in the 3-10 test conducted on the GMS W-beam design accepted by the FHWA. Therefore, I agree that test 3-10 on Single-Sided or Double Sided GMS-TB Guardrail Systems can be waived.
Further, test 3-11 on Double Sided GMS-TB Guardrail Systems would be less severe than
test 3-11 conducted on Single-Sided GMS-TB Guardrail System. Therefore, I agree that test 3-11 on Double Sided GMS-TB Guardrail Systems can be waived.
In summary, I agree that both Single-Sided and Double Sided GMS-TB Guardrail Systems, as described above, meet the appropriate evaluation criteria for NCHRP 350 TL-3 devices and may be used at all appropriate locations on the National Highway System (NHS) when selected by the contracting authority, subject to the provisions of Title 23, Code of Federal Regulations, Section 635.411, as they pertain to proprietary products.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
John R. Baxter, P.E.
File: s://directory folder/nartimovich/B156-OchoaGMS-TBfin.doc
cc: HSSD (Reader, HSA; Chron File, HSSD; N.Artimovich, HSSD; MMcDonough, HSSD)
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