Refer to: HSA-10/SS-112
Mr. Larry Mims
K & K Systems
699 Palmetto Road
Tupelo, Mississippi 38801-7662
Dear Mr. Mims:
Thank you for your facsimile messages dated June 26, July 11 and August 7, 2002, requesting Federal Highway Administration (FHWA) acceptance of variations to your company=s flashing light warning apparatus as breakaway systems for use on the National Highway System (NHS). Accompanying your letter were drawings and descriptions of the proposed modifications. You requested that we find the devices described below, and illustrated in the enclosures for reference, acceptable for use on the NHS under the provisions of National Cooperative Highway Research Program (NCHRP) Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features."
Testing of the supports was originally conducted at the Southwest Research Institute and found acceptable in FHWA Letter SS-90 dated August 18, 2000. Testing was in compliance with the guidelines contained in the National Cooperative Highway Research Program (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' (AASHTO) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals.
The original crash testing was conducted on single, four pound-per-foot u-channel posts mounted on two-bolt slip bases. The weight of the system was 192 pounds. Your current requests are for two variations:
June 26 Request
This request is to allow K&K Systems warning apparatus to be attached to spun aluminum poles, 4 inch diameter, mounted on cast aluminum breakaway transformer bases supplied by Akron Foundry, Model # TS-1000 (FHWA Acceptance Letter LS-47 dated November 19, 1997.) All equipment mounted to the pole will be placed at a height of 7 feet or higher.
July 11 Request
This request is to permit retrofit of existing warning signs in work zones with K&K Systems warning apparatus. The u-channel posts would use Marion Steel u-channel posts with the Lap Splice breakaway system. All equipment would be mounted higher than the seven foot bottom of the sign. The "B Light" system would be mounted using three threaded 5/16 inch x 2 ½ inch grade 8 plated hex bolts with flat washer and hex nuts, per post.
The crash testing conducted earlier showed very good performance for the u-channel mounted warning light system. We would expect very similar behavior for the system mounted on the aluminum pole and breakaway transformer base as long as the fastener hardware is equal or superior to that used in the crash test.
The performance of the u-channel system should also be acceptable manner, however, its performance may show more contact with the hood, windshield, and/or roof of an impacting vehicle due to the nature of u-channel posts with the lap splice than is seen with the two-bolt slip base. Because we are confident that the occupant impact speed will be within acceptable limits we find this system acceptable for retrofitting existing warning sign installations.
Because the results of testing met the FHWA requirements and the proposed modifications are not expected to cause significantly different behavior, the devices described above and shown in the enclosed drawings for reference are acceptable for use as Test Level 3 devices on the NHS under the range of conditions tested, when proposed by a State.
Please note the following standard provisions that apply to FHWA letters of acceptance:
Carol H. Jacoby, P.E.
Director, Office of Safety Design