April 1, 2004
Refer to: HSA-10/SS-124
Mr. Nick Calvi
Ultimate Highway Products, Inc.
P.O. Box 7
Stanton, California 90680
Dear Mr. Calvi:
Thank you for your letter of March 22, 2004, requesting a revision to the Federal Highway Administration (FHWA) acceptance of your company's Slip-Mate slip base for use with breakaway small sign supports on the National Highway System (NHS) under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features." The Slip-Mate was found acceptable in our letter SS-100 to Western Highway Products, dated November 21, 2001. Your present request is for acceptance of a 18-inch diameter, 42-inch deep concrete base in weak soil. Both Western Highway Products and Ultimate Highway Products, Inc., are divisions of Couch and Phillippi.
Testing of the supports was in compliance with the guidelines contained in the NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Requirements for breakaway supports are those in the American Association of State Highway and Transportation Officials' Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.
The Slip-Mate is a three-bolt omni-directional slip base system. The ½-inch triangular plates measure 6 inches on each side of the triangle. A ½-inch thick polypropylene ball bearing housing is placed between the two plates to provide reduced friction. (This is necessary for a smaller system to avoid the problem of the signpost bending before the slip base can separate.) To either slip plate is welded a 2x2 inch by 1/4 inch square steel tube. The upper tube is 18 inches long and is welded to the top slip plate to receive the 12 gage, 2 1/4 x 2 1/4 inch square perforated square steel sign support. This tube is extended so as to contact the vehicle's bumper with a significant cross-section of steel. The lower tube is 6 inches long and is welded to the bottom plate and is inserted in and fastened to the tube and sleeve combination in the foundation. The slip base bolts are ½ inch diameter x 2 ½ -inch long hex head steel bolts with nuts and washers. They are torqued to 40 foot-pounds. The anchor for the system consisted of a 2 1/4 -inch square, 36-inch long 12 gage perforated square steel tube with a 2 ½-inch square, 18-inch long 12 gage perforated strengthening sleeve with a soil stabilize bracket measuring 13 inches by 10 inches attached with two 5/16 inch corner bolts. The system was installed in the NCHRP Report 350 "Standard" soil. The Sign used in the test was a 36 x 60 inch rectangular sign attached to the support post with four 3/8 inch drive rivets. It was mounted 5 inches below the top of the 144-inch tall post. The weight of the sign and the post was 60 pounds above the slip plane.
Pendulum testing was conducted on a single sign support with the Slip-Mate system. The mass of the pendulum, which was affixed with a crushable honeycomb nose simulating a 1979 Volkswagen Rabbit, was 820 kg. The complete device as tested is shown in the Enclosure.
|Test #||Speed||Article Occup.||Speed||Delta V|
|259-1||34.5 km/hr||Uni-Mate breakaway support system||None||0.37 m/s|
Occup. Speed: Occupant Impact Speed: Speed at which a theoretical front seat occupant will contact the windshield. In meters per second
Delta V: Speed change of the test vehicle. In meters per second.
Velocity change was within acceptable limits. The stub remaining was 100 mm high as designed and within the acceptable limit. The results of the test met the FHWA requirements and the device was found acceptable.
Your present request was for acceptance of the Slip-Mate breakaway support system in an 18-inch diameter, 42-inch deep concrete foundation when used in weak soil. A concrete base of this size has been shown to provide adequate support for slip bases in weak soil areas. Because the velocity change in the test noted above was so low, we concur in your request, and find this base and foundation acceptable for use as a Test Level 3 breakaway device on the NHS under the range of conditions tested, as modified, when proposed by a State.
Please note the following standard provisions that apply to FHWA letters of acceptance:
(Original Signed By R. Powers)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety