Federal Highway Administration
1200 New Jersey Avenue, SE.
October 6, 2008
In Reply Refer To: HSSD/CC-103
Gerrit A. Dyke, P.E.
Barrier Systems, Inc.
180 River Road
Rio Vista, CA 94571
Dear Mr. Dyke:
This letter is in response to your request for Federal Highway Administration (FHWA) acceptance of a roadside safety device for use on the National Highway System (NHS).
You requested that we find this device 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.” Barrier Systems, Inc. recently purchased the rights to the U-MAD TM Truck Mounted Attenuator system from Albert W. Unrath.
Roadside safety devices should meet the guidelines contained in the NCHRP Report 350, "Recommended Procedures for the Safety Performance Evaluation of Highway Features". FHWA Memorandum “ACTION: Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.
The U-MAD™ crash cushion is comprised of an energy absorbing cartridge consisting of an aluminum and steel box structure with reinforcing materials and energy absorbing materials. The system has been successfully tested and accepted by the FHWA to the NCHRP Report 350, Test Level 3 (TL-3) and TL-2, mounted on a shadow vehicle weighing approximately 19,000 lbs (8600 kg). The truck mounting allows deployment from a 90-degree upright travel position to a horizontal configuration where it has energy absorbing capacity. The cushions are assembled in 129 inch (3.2 m) TL-3 and 78 inch (2.0 m) TL-2 lengths.
A trailer mounting system was developed for use with the U-MAD energy absorbing cartridge. Testing was conducted on this system, in accordance with the NCHRP Report 350, TL-3, to verify the performance of the U-MAD crash cushion mounted to a steel fabricated, load dampening trailer with an anti-rotation mechanism that activates upon impact. The trailer utilizes a hydraulic system mounted within the tongue to increase the ride down distance and control the engagement of anti-rotation arms with the tow vehicle. The rigid axle with torsion bar suspension can be fitted with emergency or impact activated brakes when required. The crash cushion mounts directly to the trailer and remains in the deployed (horizontal) position at all times.
The U-MAD 100K TMA was constructed from an aluminum box, having an outer shell thickness of .050 inch, with structural supports, cushion constructed into eight compartments, with each compartment containing variable cellular velocity dissipating material of varying density (CVDM). All seams are welded or steel riveted and both internally and externally sealed to prevent moisture intrusion. Additionally, each unit of crushable CVDM is contained in its own separate moisture barrier.
The U-MAD 100K TMA assembly was mounted to a two-wheel trailer which was connected to the rear of the support truck by means of a hitch. Overall length of the U-MAD 100K TMA was 10.9 feet (3.3 m). The overall weight of the U-MAD Trailer system was 2525 pounds (1147.6 kg). Individually, the trailer weighed 1617 pounds (734.8 kg), and the U-MAD 100K TMA weighed 908 pounds (412.8 kg). The support truck weighed 19, 220 pounds (8,736.2 kg).
Two full-scale tests using the 2000P vehicle were conducted on the U-MAD Trailer, the NCHRP Report 350 Tests 3-51 and 3-52. The FHWA initially only required test 3-52 to be conducted in order to assess the ability of the trailer to maintain its alignment during an off-center impact. Subsequently, all TMA trailers were required to pass test 3-51 to verify that the attenuation system was not adversely affected by the hardware needed to fabricate a trailer version. As the proposed trailer system incorporated wheels behind the basic TMA design, conversion to a trailer system was not as extensive as required by TMA trailers of other manufacturers. Copies of the test data summary sheets are enclosed for reference.
In both tests the vehicle was brought to a controlled stop without intruding into adjacent traffic lanes. Occupant impact velocities and ride down accelerations were within the recommended limits. In Test 3-51 the “shadow vehicle” to which the trailer was attached moved forward 32.5 feet (9.9 m). In Test 3-52 this roll-ahead distance was 25.6 feet (7.8 m).
Therefore, the device described in the various requests above and detailed in the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, when acceptable to a highway agency.
Please note the following standard provisions that apply to the FHWA letters of acceptance:
David A. Nicol
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