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FHWA Home / Safety / Roadway Departure / Safety Eligibility Letter

Safety Eligibility Letter CC-65E

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U.S. Department of Transportation
Federal Highway Administration

1200 New Jersey Ave. S.E.
Washington, D.C. 20590

February 13, 2009

In Reply Refer To: HSSD/CC-65E

Mr. Geoffrey Maus
Chief Design Engineer
TrafFix Devices, Inc.
160 Avenida La Pata
San Clemente, California 92673

Dear Mr. Maus:

This letter is in response to your request for the Federal Highway Administration (FHWA) acceptance of a roadside safety system for use on the National Highway System (NHS).

Name of system: Scorpion Attenuator Trailer (Modified)
Type of system: Truck Mounted Attenuator - Trailer
Test Level: NCHRP Report 350 Test Level 3
Testing conducted by: KARCO Engineering, LLC
Date of request: December 6, 2008
Date of completed package: January 21, 2009

You requested that we find this system 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.”

Requirements
Roadside safety systems should meet the guidelines contained in the NCHRP Report 350. The FHWA Memorandum “Identifying Acceptable Highway Safety Features” of July 25, 1997, provides further guidance on crash testing requirements of longitudinal barriers.

Description
The TrafFix Devices Inc. Scorpion Trailer Attenuator is a trailer based impact attenuator. It is comprised of four sections, as illustrated in the drawings enclosed for reference: the steel tongue section, the aluminum strut section, the aluminum cartridge section, and the axle wheel assembly. The steel tongue section incorporates a Telescoping Anti-Rotation System (TARS). The modified Scorpion Trailer Attenuator covered by this acceptance letter has an overall length of 5.323 m (209.6 in.), an overall width of 2.410 m (94.9 in.), and weighs a total 701.0 kg (1545 lbs).

Description of modifications:
To reduce the weight of the original Scorpion Trailer Attenuator (FHWA acceptance letter CC-65B, dated March 16, 2007), material thicknesses were optimized and in applicable locations, aluminum was used in place of steel. Changes were limited to three components: the tongue, center connecting angles, and the rear diaphragm.

  1. Reduced Trailer Tongue weight. The tongue section which incorporates the Telescoping Anti-Rotation System (TARS) was tested using thinner steel wall tubing and plate. The original heavier 3-53 tongue tested on September 27, 2006, weighed approximately 731 lbs (283 kg). The lighter 3-53 tongue tested on September 26, 2008, weighed 455 lbs (206 kg).

  2. Reduced connecting center angle weight. The set of connecting angles attach the strut and cartridge together. The original 3-53 heavier steel connecting angles tested on September 27, 2006, weighed 40 lbs (18.14 kg). The lighter 3-53 aluminum connecting angles tested on September 26, 2008, weighed 13 lbs (5.9 kg).

  3. Reduced rear diaphragm weight. The rear diaphragm consists of the attachment elements for the axle assembly and Impact Absorber Boxes A and B. The original heavier 3-53 rear diaphragm support tested on September 27, 2006, was a steel weldment and weighed approximately 170 lbs (77 kg). The lighter 3-53 rear diaphragm support tested on September 26, 2008, is an aluminum weldment and weighs approximately 65 lbs (29 kg).

The total weight reduction resulting from the three design changes is 435 lbs (162 kg).

Crash Testing
Test 3-53 was selected as a “worst case scenario” test as a result of the extreme load and stress conditions that the Trailer Attenuator components must undergo during the offset angled impact test. Test 3-53 places the modified TARS design in severe compressive and tensile stress conditions while exerting a large bending moment on the entire attenuator system about the pintle attachment point.

In comparison, a Report 350 3-52 test would impart a similar peak compression load to the favored impact side, but with significantly less angled shear load on the attenuator. A Report 350 3-51 test would impart the most total load into the attenuator, but the load would be distributed over the entire attenuator, reducing the force on each load path. The Report 3-51 test would have a minimal lateral load imparted into the attenuator.

Post crash test analysis showed that each of the modified elements – tongue, center angles, and rear diaphragm – performed in a functionally identical manner to their heavier counterparts. The modified components caused no alteration in safety performance of the trailer attenuator.

You noted that the TARS tubes did not undergo any buckling or deformation upon impact into the truck frame plate. The connecting angles and axle diaphragm contained all of their attached
components. In addition, the test results for Ride-down Acceleration and Occupant Velocity were well below the maximum allowable values and nearly equal to the original 3-53 tested values.

Findings
Therefore, the modified Scorpion Trailer Attenuator described above and detailed in the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency.

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

 

Sincerely yours,

Signature of David A. Nicol

David A. Nicol, P.E.
Director, Office of Safety Design
Office of Safety

Enclosures

Page last modified on January 17, 2013.
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