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US Department OCT 21 1696 400 Seventh St. S.W.

Washington, 0.C. 20590

Highway
Administration
Refer to: HNG~-14

Mr. Clifford M. Dent
P.O. Box 1119

Mile 16.5 North Road
Kenai, Alaska 99611

Dear Mr. Dent:

This is in response to your facsimile letter to Mr. Nicholas
Artimovich requesting Federal Highway Administration's (FHWA)
acceptance of a modification to your breakaway sign support
couplings. Our Geometric and Safety Design Acceptance Letter
SS-60, dated October 27, 1995, found 12.7-mm (-inch) and 15.9-mm
(5/8-inch) couplings acceptable in a square (4-bolt) or a
triangular (3-bolt) pattern. Your current request is to use
increased diameter bolts, namely 3/4-inch, 7/8-inch, and 1l-inch
(19.1-mm, 22.2-mm, and 25.4-mm, respectively).

In our October 27, 1995, letter we conditioned our acceptance to
sign installations "within the range of conditions tested." This
means that sign supports that are substantially weaker in bending
or more massive than the tested installation, which had a

127 x 127 x 4.76 steel tube support and a mass of 70.8 kg, would
not be acceptable without further testing. The larger bolt sizes
you wish to use are typically used with larger supports than
those tested. The 4.5-m/s velocity change of the support tested
with the 15.9-mm (5/8-inch) bolt is close to the acceptance
limit, and a more massive installation may fail to meet the

5.0 m/s maximum allowable velocity change.

You have stated to Mr. Artimovich that some States have "over
designed" their breakaway bases and use larger diameter

bolts than are necessary to adequately support their sign
installations. Some of these States wish to use your company's
necked-down bolt in bases that were made for bolts larger than
the two sizes of your bolt already found acceptable. We further
understand that the larger bolts you wish to sell are only
intended for use on sign installations of similar mass to those
that were tested. With this understanding, we are willing to
accept the use of the necked-down 3/4-inch, 7/8-inch, and l-inch
(19.1-mm, 22.2-mm, and 25.4-mm) bolts, for three- or four-bolt,
horizontal matched-plate bases subject to the following
conditions:

1. Maximum mass per foot of sign post shall not exceed
30 kg/m (20 pounds per foot.)


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2. Maximum mass of sign and support shall not exceed 100 kg
(220 pounds).

3. Maximum perpendicular distance from a line connecting
any two adjacent bolts to a parallel line through a
third does not exceed 155 mm. (This will yield various
maximum bolt circle diameters, depending on the bolt
pattern (triangular, square, or rectangular) used.)

4. Maximum diameter at the grooved section shall not exceed
9.65 mn.

5. The mated plates are at least as stiff as the tested
plates.

Because the material specifications of your galvanized, ASTM
A325-type-material, steel bolts and the diameter of the critical
necked-down section will not be changed, we concur in the use of
the 19.1-mm, 22.2-mm, and 25.4-mm necked-down bolts on the
National Highway System if requested by a State. All other
conditions in our October 27, 1995, letter remain in effect.
Dimensions of all seven acceptable necked-down bolts are given in
the enclosed table and shown in the enclosed drawings.

Sincerely yours,

Seppo I. Sillan, Acting Chief
Federal-Aid and Design Division

Enclosures

Supplemental ¢
Letter ss-60q eometric and Roadside Design Acceptance.
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