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U.S. Department of Transportation

Federal Highway Administration

400 Seventh St., S.W.
Washington, D.C. 20590


April 22, 2005

Refer to: HSA-10/WZ-207

Mr. Jan Miller
TrafFix Devices
220 Calle Pintoresco
San Clemente, California 92672

Dear Mr. Miller:

Thank you for your letter of March 23, 2005, requesting the Federal Highway Administration (FHWA) acceptance of your company's Tri-Buster Safety Tripod stand supporting a plywood sign as a crashworthy traffic control device for use in work zones on the National Highway System (NHS). Accompanying your letter were reports of crash testing conducted by Karco Engineering and video of the test. You requested that we find this stand acceptable for use on the NHS under the provisions of the National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."


The FHWA guidance on crash testing of work zone traffic control devices is contained in two memoranda. The first, dated July 25, 1997, titled "INFORMATION: Identifying Acceptable Highway Safety Features," established four categories of work zone devices: Category I devices are those lightweight devices which are to be self-certified by the vendor, Category II devices are other lightweight devices which need individual crash testing but with reduced instrumentation, Category III devices are barriers and other fixed or heavy devices also needing crash testing with normal instrumentation, and Category IV devices are trailer mounted lighted signs, arrow panels, etc. for which crash testing requirements have not yet been established. The second guidance memorandum was issued on August 28, 1998, and is titled "INFORMATION: Crash Tested Work Zone Traffic Control Devices." This later memorandum lists devices that are acceptable under Categories I, II, and III.

A brief description of the devices follows:

The Tri-Buster is a "triangular footprint" or "tripod" portable sign stand with a galvanized steel upright support measuring 1.25 inches square with a wall thickness of 0.070 inches. A 1 inch steel inner mast extends out to a total height of 73 inches supporting a 48" x 48" diamond sign at approximately 13 inches above the pavement. The mast is supported on three 1.25 inch square steel folding legs which form an upper joining "heart-plate" which is attached to the telescoping inner mast. The inner mast is adjusted to the top section of the diamond sign that pushes the bottom of the sign against two lower steel mounts. The weight of the tested Tri-Buster sign stand with plywood diamond sign is 48 pounds.


Full-scale automobile testing was conducted on your company's devices. Two stand-alone examples of the device were tested in tandem, one edge-on and the next placed six meters downstream turned at 90 degrees for a head-on impact, as called for in our guidance memoranda. The test is summarized in the table below.


NCHRP Report 350 Test 3-71

Stand Orientation

90 degrees

Head on

Sign Stand Tested

Tri-Buster with 48” x 48” x 5/8” plywood sign

Weight of Tested Stand

72 pounds

Mounting heights

13 inches

13 inches

Flags? Lights?



Mass of Test Vehicle

905 kg

Impact Speed

98.2 km/hr/  (61.1 mph)

Velocity Change

2.1 km/hr, or 0.6 m/sec (max of 5 m/sec allowed)

Occupant Comp. Def.

1 inch windshield deformation

Extent of contact

Minor contact damage to bumper, grille, hood, roof, glass

Windshield Damage

None, sign went over

Moderate cracking

Other notes

Head-on: Sign broke into pieces and cracked windshield.

Damage to the windshield was moderate but there was no penetration of the glass, and the driver's view was not obscured. The damage resulted from the head-on impact. In the 90 degree impact the front of the car contacted the lower leading edge of the sign causing it to rotate. The leading corner of the sign contacted the hood and base of the windshield, which propelled the sign up in the air and over the vehicle.


Request 1: Acceptance of the TDI Tri-Buster sign stand for use with the tested 48" x 48" x 5/8" plywood signs, including signs of smaller size and thinner/lighter plywood materials.

Request 2: Acceptance of the TDI Tri-Buster sign stands for use with additional sign sizes at the tested 13" mounting height. The following substrates and sizes are requested:


The results of the testing met the FHWA requirements and, therefore, the devices described in Request 1 are acceptable.

We concur in Request 2 as the proposed shaped signs would also engage the vehicle front end early in the crash event and are likely to perform in a similar manner to the tested signs.

In summary, the Tri-Buster stand, shown in the enclosed drawings for reference, supporting signs of the sizes and materials detailed above, is acceptable for use on the NHS under the range of conditions tested, when proposed by a State.

Please note the following standard provisions that apply to the FHWA letters of acceptance:

Sincerely yours,

John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety


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