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U.S. Department of Transportation

Federal Highway Administration

400 Seventh St., S.W.
Washington, D.C. 20590

July 7, 2006

In Reply Refer To: HSA-10/SS-139

Mr. Clifford Dent
P.O. Box 6007
Farmington, New Mexico 87499

Dear Mr. Dent:

Thank you for your letter sent May 12 requesting the Federal Highway Administration’s (FHWA) acceptance of your company’s fuse plate for use with breakaway sign supports on the National Highway System (NHS). Based on full scale crash tests of generic perforated fuse plates by others and static testing that compared your design with the generic design, you requested that we find Dent Fuse Plates acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features.”

Many States have found that slotted fuse plates slip and fail under some wind and vibration conditions. The generic perforated fuse plates developed by Texas to solve this problem do not always release completely upon vehicle impact. The Dent Fuse Plate is an attempt to improve the breakaway performance of crashworthy sign supports while avoiding unintended sign “blow downs” in high winds.

Accompanying your letter was a report by Exponent Failure Analysis Associates of static laboratory testing of your fuse plate design and of the generic perforated fuse plates. Both were tested on the following sizes of wide flange steel beams:

S4 x 7.7
W6 x 9
W6 x 15
W8 x 18

In each case the force required to release your fuse plate was less than that required to release the generic design. This indicates that the breakaway performance of these wide flange posts mounted on approved breakaway supports would be improved using Dent Fuse Plates. As you discussed with Mr. Artimovich of my office, we would still recommend that full-scale automobile or bogie testing (not pendulum) of a dual-leg wide-flanged signpost installation be conducted with a production model Dent Fuse Plates in place in the near future.

The Dent Fuse Plates, as shown in the enclosed drawings for reference are acceptable for use as Test Level 3 devices on the NHS under the conditions noted above, when proposed by a State. The plate designed for the S-3 x 5.7 post will also be acceptable for use. The W6 x 9 Plate will also be acceptable when modified to be used with the 4 x 4 inch square tube sign support.

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

Sincerely yours,

John R. Baxter, P.E.

John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety                                          


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