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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter B-150A

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U.S. Department of Transportation
Federal Highway Administration

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

March 26, 2008

In Reply Refer To: HSSD/B-150A

Mr. Andrew Artar
Vice President Sales and Marketing
Gregory Highway Products
4100 13th Street, SW
Canton, OH 44710

Dear Mr. Artar:

This is in response to your letter of November 1, 2007, requesting the Federal Highway Administration’s (FHWA) acceptance of your company’s single- and dual-face w-beam Gregory Mini Spacer (GMS) Guardrail Systems as a test level 3 (TL-3) device for use on the National Highway System (NHS). Accompanying your letter were reports of crash testing conducted by Southwest Research Institute. You requested that we find this device acceptable for use on the NHS under the provisions of the forthcoming American Association of State Highway and Transportation Officials Manual on Assessing Safety Hardware-2008 (MASH08), which is expected to supersede Report 350 in the near future.

Introduction
The FHWA guidance on crash testing of roadside safety hardware is contained in a memorandum dated July 25, 1997, titled “INFORMATION: Identifying Acceptable Highway Safety Features” and recognizes National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features” as the current crash test guidance. The Gregory Highway Products has chosen to anticipate the adoption of MASH08 by testing with the 2270P vehicle, an option that FHWA has offered with the understanding that testing may need to be done over if changes to the test criteria are made before MASH08 is formally adopted.

The GMS system was found acceptable under NCHRP Report 350 criteria in our FHWA acceptance letter B-150 dated October 27, 2006. Your present request is for MASH08 acceptance of the same barrier system, described as follows:

The GMS system consists of 12-gauge steel W-beam panels mounted directly onto standard, unmodified 6-foot long W6 x 8.5 steel posts with no offset blocks or backup plates, spaced at 6 feet 3 inches and with a top-of-rail height of either 31 inches or 27 5/8 inches. The rail was attached to each post using a 5/16-inch diameter standard hex head bolt incorporated into a proprietary releasable fastener called a “GMS” that enables conventional guardrail and posts to perform without the need for offset blocks.

The two test summary sheets using the 2270P vehicle, one each for the 27 5/8 inch height (Test GMS-4) at TL-2 and one for the same mounting height (Test GMS-6) at TL-3, are enclosed for reference. Testing with the 820C vehicle on the 31 inch dual-face w-beam barrier having two splices at every other post had been conducted under the initial testing (Test GMS-2) and is considered a “worst case scenario” as it used a lighter vehicle than called for in MASH08 potentially subjecting vehicle occupants to higher impact forces, especially since there were two rail connections at each post contacted by the vehicle.

Testing
Full-scale automobile and pickup testing has been conducted on the GMS barrier. Tests GMS-1 and GMS-2 supported FHWA acceptance letter B-150. Tests GMS-4 and GMS-6 were conducted to support the present request. The GMS-4 was intended to be a TL-3 test but a testing malfunction resulted in inadequate impact speed and re-run as GMS-6. Selected barrier and crash test details, including dynamic deflection, are summarized in the following table.

Test # Test Designation Barrier Height* Barrier Deflection**
GMS-1 MASH08 TL-3 / 3-11 31 inches. Single faced. 2.92 ft
GMS-2 Report 350 TL-3 / 3-10 31 inches Dual faced 2.20 ft
GMS-4 MASH08 TL-2 / 2-11 27-5/8 inches Single faced 2.25 ft
GMS-6 MASH08 TL-3 / 3-11 27-5/8 inches Single faced 4.33 ft

* Height to top of rail.
** Maximum dynamic deflection. Our current criteria sets the “design deflection distance” at the maximum dynamic deflection recorded in Report 350 test 3-11. From the crash testing you performed and your analysis (a method that agrees with a tuned Barrier VII analysis), you came up with recommended Report 350 test 3-11 (2000P) deflection criteria. You recommend that the minimum distances at which the face of a GMS installation be placed from the face of a rigid obstacle (e.g., bridge pier or overhead sign support) be 1.25 m (49 inches), 1.12 m (44 inches), and 0.90 m (35 inches) for standard (6 ft 3 inch), 1/2, and 1/4 post spacing, respectively. These offsets are based on the “working width” deflections seen in the crash tests/analysis and include some degree of pickup truck penetration beyond the vertical plane of the barrier’s dynamic deflection. As with all traffic barriers, larger offset distances would be required to shield similar features from vehicles with higher centers of gravity, such as single-unit trucks or buses, because of the relatively high roll angles seen with these vehicles in rigid and semi-rigid barrier tests of similar height.

Findings
As noted in the enclosed test data summary sheets the test vehicles were smoothly redirected and met occupant impact force and occupant compartment deformation criteria. Therefore, the system described above is acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to the contracting authority. You also requested the following be included in this acceptance letter:

We concur in these variations for both single face and dual face installations.

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

 

Sincerely yours,

David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Page last modified on August 16, 2011.
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