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United States Department of Transportation

FHWA Highway Safety Programs

Safety Eligibility Letter SS-17

Hardware Type:

Sign Supports, Mailboxes, and Delineator Posts

Code:

SS-17

Date:

01/08/1990

Testing Criteria:

NCHRP 350

Manufacturer:

Transpo Industries

Device Description:

Type A and Type B breakaway couplings.(If installed by direct burial, then Type AUX for S-1 soil only.)
(Posts limited to 45 #/ft below the hinge.)

View PDF:

ss17.pdf (744.07 KB)

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January 8, 1990

Refer to: HNG-14/SS-17

Mr. Arthur M. Dinitz
President
Transpo Industries, Inc.
20 Jones Street
New Rochelle, New York 10801-6024

Dear Mr. Dinitz:

This is in response to your October 13 letter to Mr. Thomas O. Willett requesting acceptance of your company's Break-Safe breakaway sign support system for use on Federal-aid highway projects. Transmitted with your letter was the Southwest Research Institute report (dated September 1989) of the pendulum tests you had performed, and drawings of the Type A and Type B systems. Additional information including drawings, were submitted with your December 13, 1989, letter.

The tests were conducted to assess the compliance of the Break-Safe frangible couplings with the breakaway requirements of the 1985 American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals. These specifications have been adopted, with minor modifications by the Federal Highway Administration (FHWA). Testing was conducted using a 1,800 pound instrumented pendulum with a 10 stage crushable nose. The speed of the pendulum at impact was 20 m.p.h. (29.3 fps) in each case. The tests and their results are summarized below. Al impacts are head on except as noted for test TP-7.

Test No.	Test Article Description	Total Weight (lbs)	20 mph Test Velocity Change (fps)	60 mph Calc Velocity Change (fps)	Stub Height (in)
TP-4	B-525 Coupling, W8x18 Post	297	4.1	4.9	0.3
TP-5	B-650 Coupling, W12x35 Post	595	5.7	10.7	0.3
TP-6	AI6 Coupling, W6x9 Post	98	1.6	4.1	0.3
TP-7	B-525 Coupling, W8x18 Post (45 degree hit)	297	2.8	4.4	0.3
TP-8	AUX8 Coupling, Back to Back Franklin Steel, 4 pounds per foot U-post in "strong" soil	110	2.3	2.4	4.0

These results meet the change in velocity and stub height requirements adopted by the AASHTO and the FHWA. Therefore, except as limited below, your company's Break-Safe Type A and Type B couplings are acceptable for use on Federal-aid highway projects, if proposed by a State. We note the AUX system using back to back U-posts was only tested in the strong (National Cooperative Highway Research Program (NCHRP) designation S-1) soil described in the NCHRP Report 230. Embedding the stub in "weak" (S-2) soil may allow the post and stub to rotate under impact, loading the couplings in a way that they do not readily fracture. Therefore, testing in "weak" soil is recommended to fully qualify the AUX Brake-Safe systems. Until the direct burial Type AUX systems are qualified in the S-2 soil, our acceptance is only extended for their use in "strong" soils.

Additionally, we note that all the tests were run on single support installations with ballast attached to the upper portion of the support, but with no sign blank or upper hinge present. This is an unconventional and questionable test procedure. If the occupant risk test results were not so low we would request that tests be run on multiple support installations before accepting the use of the subject couplings in such installations. Your request that acceptance be granted for "any size or weight per foot provided the mass of the post under hinge mechanism is 600 pounds or less." Since upper hinge/slip plate mechanisms were not involved in your tests, we are unable to confirm that such a mass would yield acceptable results. However, we believe that for installations where supports are further than 7 feet apart, posts up to 45 pounds per foot will perform satisfactorily (we have applied the same size limitation to slip-base sign supports). For dual support installations (where both the posts lie within a 7-foot path), we limit our acceptance to situations where the total weight of both posts below the hinges ifs 45 pounds per foot. The couplings should not be used in sign structures with three supports or more if posts are closer than 7 feet apart without further testing.

Our acceptance is limited to he breakaway characteristics of the systems and does not cover their structural features. Presumably, you will supply potential users with sufficient information on structural design and installation requirements to ensure proper performance. We anticipate that the States will require certification from Transpo Industries that the hardware furnished has essentially the same chemistry, mechanical properties, and geometry as those used in the tests, and that they will meet the FHWA breakaway requirements.

Since the Break-Safe couplings are proprietary items, to be used in a Federal-aid highway project they: (a) must be supplied through competitive bidding with equally suitable unpatented items; (b) the State highway agency must certify that they are essential for synchronization with existing highway facilities or that no equally suitable alternate exists; or (c) they must be used for research or for a distinctive type of construction on relatively short sections of road for experimental purposes. Our regulations concerning proprietary products are contained in Title 23, Code of Federal Regulations, Section 635.411, a copy of which is enclosed.

Sincerely yours,

L. A. Staron, Chief
Federal-Aid and Design Division

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