U.S. Department 

Of Transportation 

Federal Highway 

Administration

400 Seventh St., S.W. 

Washington, D.C. 20590 

July 15, 1992 

Refer to: HNG-14/SS-29 

Mr. William G. Edwards 

A.B Chance Company 

210 North Allen Street 

Centralia, Missouri 65240-1395 

Dear Mr. Edwards: 

This is in response to your request for the Federal highway Administration’s (FHWA) 

acceptance of your company’s helical screw foundations (HSFs) as foundations for slipbase supports for motorist aid call boxes. Your initial letter of November 26, 1991, 

included the reports of crash tests Chance 1 and Chance 2 conducted by Southwest 

Research Institute (SWRI) along with documentation describing the foundations. You 

provided additional information and video of the callbox support crash testing with your 

March 10 letter responding to our request of January 2. Subsequent to our meeting on 

May 27 you submitted a copy of a crash test conducted in “weak” soil by Mobility 

Systems and Equipment Company (MSE) and followed that up with final details in your 

facsimile message of July 6. 

The tests were conducted to assess the breakaway performance of steel-post motorist-aid 

call boxes mounted on HSFs. Requirements for breakaway supports are found in the 

1985 AASHTO Standard Specifications for Structural Supports for Highway Signs, 

Luminaires and Traffic Signals. These specifications have been adopted, with minor 

modifications, by the FHWA. The test articles are described in the enclosed drawings. 

The test results are summarized here: 

Test Number SWRI 

Chance-1

SWRI

Chance-2

MSE

Test-1

Support Type Sch. 40 

Steel 

Sch. 40 

Steel 

Steel .266 

wall 

Test Article Mass, kg (lbs.) (including 23.6 

kg callbox) 

95 (208) 95 (208) 100 (218) 

Bolt Torque, N-m (ft-lbs) 40.7 (30) 40.7 (30) 67.9 (50) 

Vehicle Mass, kg (lbs) 898 (1975) 890 (1957) 825 (1815) 

Soil Type (per NCHRP 230) S-1 S-1 S-1 
Impact Speed, km/hr (mph) 30.9 (19.2) 95.1 (59.1) 31.5 (19.6) 

Velocity Change, m/s (fps) 0.37 (1.2) 1.28 (4.2) 1.28 (4.2) 

Stub Height, mm (in) 75 (3) 75 (3) 100 (4) 

All supports were steel poles, 100 mm (4 inches) in diameter with a height of 4300 mm 

(14 feet) to the top of the pole (base of antenna). The HSF was embedded 1500 mm (5 

feet) into the soil. We believe that the low speed test in weak soil is a “worst case” 

scenario and that a high speed test is not warranted. 

The films of the crash tests that you supplied show that the only significant damage to the 

test vehicles occurred when the top of the support rotated after impact and struck the rear 

hatch windows. We do not consider this to be significant passenger compartment 

intrusion. The comparison test video that you provided showed that a wooden callbox 

support, when tested, broke at the groundline, at bumper height, and below the call box. 

This left the callbox suspended in space, with the result that it severely damaged the 

windshield of the test vehicle and entered the passenger compartment. It is apparent that 

a different type support, such as a steel pipe, is required to assure that the callbox does 

not become a greater hazard than the support in the event of a crash. 

The results of the three slip-base tests outline above meet the change in velocity and stub 

height requirements adopted by AASHTO and the FHWA. Therefore, your company’s 

helical screw foundation described above is acceptable for use on Federal-aid highway 

projects to support slip-base callbox supports, within the range of conditions tested, if 

proposed by a State. 

Our acceptance is limited to breakaway characteristics of the system and does not cover 

its 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 A.B. Chance 

Company and/or the callbox supplier that the hardware furnished has essentially the same 

chemistry, mechanical properties, and geometry as that used in the tests, and that it will 

meet the FHWA change in velocity requirements. 

 Sincerely yours, 

 Lawrence A. Staron, Chief 

 Federal-Aid and Design Division 

Enclosures 

Geometric and Roadside Design Acceptance Letter SS-29