U.S. Department 

Of Transportation 

Federal Highway 

Administration

400 Seventh St., S.W. 

Washington, D.C. 20590 

February 3, 1998 

Refer to: HNG-14/SS-78 

Mr. Frank T. Ellis 

Highway Post Sales 

SMI Steel-Southern Post Company 

14340 Torrey Chase Boulevard- Suite 360 

Houston, Texas 77014 

Dear Mr. Ellis: 

 This is in reply to your January 13 letter to Mr. Henry Rentz regarding your company’s 

steel flanged channel sign posts. You requested that your 3.0-kg/m (2.0-lb/ft) and 3.7-

kg/m (2.5-ol/ft) posts meeting the requirements of ASTM A499-81 (re-rolled rail steel), 

Grade 60, be found acceptable for use on the National Highway System (NHS) where 

breakaway supports are required. You requested that one or two posts be acceptable 

within a 2.1-meter span when buried directly into strong soil, and up to 3 posts be found 

acceptable within a 2.1meter span when used with an overlap splice. In addition, you 

indicated that the spliced posts require soil plates on the stubs when used in “weak” soil. 

Drawings of the post sections are enclosed. You described your lap-splice hardware as 

follows: 

1. Spacers: 25.4-mm (1.0-inch) diameter x 15.876-mm (0.625-inch) thick with 

11.125-mm (0.438-inch hole), zinc plated; 

2. Bolts: Hex head, fully threaded Grade 9, 7.9375-mm (5/16-inch) – 18 UNC x 1.5-

inch (38-mm); 

3. Nuts: Hex head, integral flanged lock nut, or standard Grade 9 hex head nut and 

lock washer. 

The soil plates required in weak soil are to have a minimum size of 360 mm x 360 mm 

and 6.3 mm thick. 

The following table summarizes the range of acceptable installations that have been 

tested using re-rolled rail steel U-channel supports: 

Summary of Prior Testing on 4.5-kg/m (3lb/ft) U-Channel Posts 

 Strong Soil 

Direct Bury 

Strong Soil 

Spliced* 

Weak Soil 

Direct Bury 

Weak Soil 

Spliced* 
One Post Yes Yes No Yes** 

Two Posts Yes*** Yes No Yes** 

Three Posts No Yes No Yes** 

Notes: 

*Spacers used in U-Channel overlap splices were internally threaded. The bolts in the 

splices were spaced at 100-mm center to center. 

**Full scale testing has been done in weak soil on a spliced triple-post U-Channel 

support with soil plates on each base post. These soil plates (minimum size of 360 mm x 

360 mm x 6.3 mm thick) are necessary for breakaway purposes when spliced U-channel 

supports are used in weak soil. 

***A 1995 test of this configuration with a 1.5-m sign mounting height resulted in 

unacceptable roof and windshield deformation (velocity change was acceptable). 

Therefore, a minimum mounting height of 2.1 m to the bottom of the sign, as is 

recommended for all breakaway sign support installations, is necessary to avoid large 

passenger compartment deformation. 

Your company’s posts, fastener hardware, and soil plates are equivalent to breakaway 

supports previously found acceptable. Therefore, your company’s 3.0-kg/m and 3.7-kg/m 

U-channel sign supports, conforming to ASTM A499-81, Grade 60 steel and the 

configurations outlined in the table above, are acceptable for use on the NHS, subject to 

the conditions cited, when requested by a State. 

Our acceptance is limited to the breakaway characteristics of the supports 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 SMI Steel that 

the posts furnished have essentially the same chemistry, mechanical properties, and 

geometry as those you have described to us, and that they will meet the Federal Highway 

Administration change in velocity requirements. 

Sincerely yours, 

Dwight A. Horne 

Chief, Federal-Aid and Design 

Division 

Enclosure 

Geometric and Safety Design Acceptance Letter SS-78