U.S. Department 

Of Transportation 

Federal Highway 

Administration

400 Seventh St., S.W. 

Washington, D.C. 20590 

March 31, 1989 

Refer to: HNG-14/SS-08 

Mr. Ellwood Irish 

Chief Engineer 

Unistrut Corporation 

Eisenhower Plaza – Suite 600 

777 East Eisenhower Parkway 

Ann Arbor, Michigan 48108 

Dear Mr. Irish: 

This is in response to your February 17 letter to Mr. James H. Hatton requesting Federal 

Highway Administration (FHWA) acceptance of single and dual support installations of 

your company’s Telespar Highway Sign Posts. You enclosed copies of the report FullScale Mini-compact Vehicle Tests on Telespar Sign Supports in Strong and Weak Soil

and Addendum dated August 1987, and September 1988, respectively. 

The support system consists of perforated square steel tube sign supports inserted into 

and bolted to larger tubes driven to within approximately 1 1⁄2 inches of the ground 

surface. Tube sizes and gauges vary depending on sign loading requirements. 

Five vehicle crash tests were conducted on 2 1⁄2-inch, 10-gauge square tubes (24H12) by 

the University of Nebraska (UNL) on single posts. Two additional tests were conducted 

by UNL on dual posts made of 2-inch, 12-gauge square tubes (20F12). 

The test results are summarized below: 

Test 

No. 

Post 

Part 

No. 

Support 

Number 

Car 

Weight 

lbs. 

Type 

Soil 

Embedment 

Depth Inches 

Car 

Speed 

M.P.H. 

Change in 

Speed 

F.P.S. 

1 24H12 Single 1840 Strong 34 20.2 12.8 

2 24H12 Single 1840 Strong 34 62.2 11.7 

3 24H12 Single 1840 Weak 54 20.2 12.5 

4 24H12 Single 1840 Weak 54 60.6 5.1 

5 20F12 Dual 1840 Weak 54 20.1 14.8 

6 20F12 Dual 1840 Strong 34 20.1 14.0 

* 24H12 Single 1800 Weak 34 20.8 12.5 
*This test resulted in the base post being pulled from the soil. For the subsequent retest, 

test number 3, the embedment length was increased to 54 inches. (Per March 20 

correspondence from Dr. Edward R. Post, UNL.) 

Testing conformed to the recommendations of NCHRP Report 230. All tests met the 

velocity change criteria of the AASHTO Standard Specifications for Structural Supports 

for Highway Signs, Luminaires, and Traffic Signals, 1985. However, test number 2, in 

which the sign and post caused significant damage to the test vehicle’s roof, requires an 

additional assessment. The NCHRP Report 230 does not define an unacceptable level of 

occupant compartment intrusion. We have judged the results of test number 2 as 

marginal, but not sufficient to deny acceptance of the system. 

The steel used in the tested posts was ASTM Specification A446, Grade A, Designation 

G-90, which you use for fabricating galvanized posts. Your “Permagreen” finish posts 

are fabricated from ASTM Specification A570, Grade 33 steel. Which we conclude will 

have breakaway characteristics comparable to the tested materials. 

Based on the above information, we conclude that the tested system, as well as the 

system using A570 steel, meets the breakaway requirements of both the 1975 and the 

1985 editions of the American Association of State Highway and Transportation Officials 

(AASHTO) “Standard Specifications for Structural Supports for Highway Signs, 

Luminaires and Traffic Signals.” Therefore, the system is acceptable for use on Federalaid highway projects within the range shown below for both strong and weak soils, if 

proposed by a State. 

Post No. Size Inches Gauge Number Permitted Within 7-foot Path 

24H12 2 1⁄2 10 1 

21H12 2 3/16 10 1 

24F12 2 1⁄2 12 1 

22F12 2 1⁄4 12 1 

20F12 2 12 2 

16F12 1 3⁄4 12 2 

14F12 1 1⁄2 12 2 

This acceptance is limited to breakaway characteristics of the system described above and 

does not cover its structural features. Presumably, Unistrut Corporation will supply 

potential users with sufficient information on structural design and installation 

requirements to ensure proper support performance. 

We anticipate that the States will require certification from Unistrut Corporation that 

materials furnished have chemistries, mechanical properties, and geometries consistent 

with materials used in the tests and that the supports made from the materials will meet 

the breakaway requirements of the AASHTO specifications. 

 Sincerely yours, 
 L. A. Staron, Chief 

 Federal-Aid and Design Division