U.S. Department 

Of Transportation 

Federal Highway 

Administration

400 Seventh St., S.W. 

Washington, D.C. 20590 

July 13, 1995 

Refer to: HNG-14/SS-56 

Mr. Rick Mauer 

National Sales Manager 

Marion Steel Company 

912 Cheney Avenue 

Marion, Ohio 43303 

Dear Mr. Mauer: 

Thank you for your April 12 letter requesting that the Federal Highway Administration 

(FHWA) accept your company’s “Lap Splice” breakaway system for Rib-Bak u-channel 

sign supports. Your letter was accompanied by the report Evaluation of the Crash 

Performance of Triple Stel U-Channel Sign Support Installations in Weak Soil by the 

Texas Transportation Institute (TTI), dated March 1995, which has since been 

supplemented by a draft strong soil test report from TTI dates June 1995. You provided 

additional information by facsimile on June 30. 

Full-scale crash testing was done in accordance with the National highway Cooperative 

Research Program Report 350 Recommended Procedures for the Safety Performance

Evaluation of Highway Features. Requirements for the breakaway supports are found in 

the American Association of State Highway and Transportations Officials’ (AASHTO) 

Standard Specifications for Structural Supports for Highway Signs, Luminaires and

These specifications have been adopted by the FHWA. 

You requested comprehensive acceptance or your sign support system based on the lowspeed tests in S-2 (“weak”) soil only. While this soil and speed combination is usually 

considered a “worst case” for testing small sign supports, some spliced u-channel 

supports failed when test in S-1 (“strong”) soil. Therefore we requested that you run a 

test in S-1 soil also. We received the draft strong-soil TTI report on June 22. 

Three tests were conducted on triple post installations directly buried in soil, one for each 

of two sizes of u-channels in weak soil and one for the larger of the two u-channels in 

strong soil. The supports were constructed from Marion Steel SP-80 Rib-Bak, 4.5-kg/m 

(3.0 pound/foot) and 6.0-kg/m (4.0 pound/foot) steel u-channel sign supports. One-meter 

(3.2 –foot) long ground supports (stubs) were driven so that their tops were 25 mm above 

the ground line in both weak-soil tests and 100 mm above the ground line in the strong-
soil test. (Stubs and supports were made of the same weight u-channels.) A 150-mm (6 

inch) Lap Splice was used to connect the sign support to the ground support stub. The 

Lap Splice consists of high strength Grade 9 bolts, self locking flange nuts, Grade 9 cut 

washers, and threaded spacers. The bolts are 100 mm (4 inches) apart, securing the 

support to the back of the stub. The spacers separate the webs of the stub and sign post to 

prevent post deformation during tightening of the splice bolts. The spacers are 9 mm 

(0.75 inches) square and drilled and tapped for an 8-mm (5/16-18 UNC) bolt. The soil 

plates, when used, were 305 mm (12 inches) wide at the top, 152 mm (6 inches) wide at 

the bottom, 152 mm (6 inches) high and 3 mm (0.12 inches) thick, with their tops located 

just below the ground line. 

Test Number: 

270687- 

- MAR-1 -MAR-2 -MAR-3 

Test Article 4.5 kg/m 6.0 kg/m 6.0 kg/m 

Soil Type Weak Weak Strong 

Soil Plates Used? No Yes No 

Vehicle mass, kg 

(lbs.) 

820 (1808) 820(1808) 820 (1808) 

Impact Speed, 

km/h 

34.6 (21.5) 34.2 (21.2) 35.0 (21.7) 

Vehicle Delta V 

m/s (ft/s) 

5.8 (19.1) * 3.9 (12.8) 6.3 (20.6) * 

Est. High Speed 

Delta V m/s (ft/s) 

1.3 (4.3) 1.2 (3.1) 1.8 (5.8) 

Occupant Imp. 

M/s (ft/s) 

3.6 (11.8) 3.2 (10.5) 4.9 (16.1) 

Maximum Stub 

Height, mm (in) 

267 (10.5) ** 178 (7.0) ** 100 (4.0) 

Failure Mode All 3 posts 

broke at bumper 

height. 

All 3 Posts broke at 

bumper, two splices also 

separated. 

One post broke at bumper 

height. Splices separated on 

the other two. 

*Although the vehicle speed change exceeded the recommended limit of 5.0 m/s, the critical 

occupant impact speeds were within the 5.0 m/s requirement. 

** Some portions of signposts exceeding the 100-mm height limit remained attached to the 

stubs, but they were easily traversed by the test vehicle and not considered hazardous. 

The results of these tests meet the change in velocity and stub-height requirements adopted 

by ASSHTO and FHWA. Earlier testing by TTI for the Arizona Department of 

Transportation confirmed that the spliced triple-post installation of 4.5 kg/m Marion RibBak posts performed in an acceptable manner when tested in strong soil (no soil plate 

needed). This was the subject of our acceptance letter dates August 31, 1989, (Number SS13.) 

Therefore, the 4.5- and 6.0-kg/m Marion Steel Rib Back sign supports with lap Splice 

connections will be acceptable for use on the National Highway System (NHS), under 

condit8ions comparable to those evaluated, when selected by a highway agency. The 

support stubs are to be embedded in soil, with 6.0-kg/m supports requiring soil plates when 

installed in weak soil. Soil places may be used with 4.5-kg/m supports if an agency 
desires. One, two, or three of these supports may be placed within a span of 2.1 m. The 

minimum clearance between the bottom of the sign panel and the ground line is to be 2:1 

m. 

Because the Marion Steel Lap Splice is proprietary, to be used in Federal-aid highway 

projects, except exempt non-NHS projects: (a) It must be supplied through competitive 

bidding with equally suitable unpatented items; (b) the highway agency must certify that it 

is essential for synchronization with existing highway facilities or that no equally suitable 

alternate exists; or (c) it 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, 

 Jerry L. Poston, Chief 

 Federal-Aid and Design Division 

Enclosure 

Geometric and Roadside Design Acceptance Letter Number SS-56