Federal Highway Administration
400 Seventh St., S.W.
March 16, 2007
In Reply Refer To: HSSD/CC-65B
Mr. Felipe Almanza
Mr. Jan Miller
TrafFix Devices, Inc.
220 Calle Pintoresco
San Clemente, California 92672
Dear Mr. Almanza and Mr. Miller:
In your December 20, 2006 letter to Mr. Nicholas Artimovich of my staff you requested the Federal Highway Administration (FHWA) acceptance of a modified version of your existing Scorpion C 10,000 truck-mounted attenuator (TMA), specifically a new trailer version with wheels and a towing hitch You refer to this unit as the Scorpion Trailer Attenuator and request it be accepted for use as a National Cooperative Highway Research Program (NCHRP) Report 350 device at Test Level 3 (TL 3) utilizing the rear axle configuration, for use with host vehicles weighing in the range between 10,000 pounds and 20,000 pounds. To support your request you submitted drawings and test reports prepared by KARCO Engineering Automotive Research Center in Adelanto, California, and crash test videos. Additional information in response to our request was provided on March 14, 2007.
You stated that the Scorpion Trailer Attenuator utilizes the same curved aluminum tube framework and engineered aluminum crush modules as the original Scorpion C 10,000 TMA previously submitted to our office for acceptance (reference FHWA letter HSA-10/CC65 & 65A). The total length of this Trailer Attenuator is 17.3 feet (5.3 m) including the steel tongue section which attaches the trailer. The total Scorpion Trailer Attenuator weight of approximately 1,900 pounds includes the 1,260 pound Trailer Attenuator and 640 pound steel tongue trailer attachment. Two modifications were made to the Scorpion C 10,000 TMA: (1) a rear mounted axle with tire assembly attached to a steel diaphragm at the rear cartridge, and (2) the steel tongue section that provides the trailer attachment point which incorporates an anti-rotation feature that is activated in the event of an impact. These modifications are displayed in the enclosed drawings. When impacted, the steel tongue is specifically designed to prevent the Attenuator Trailer from rotating about the pintle hook and the rear of the host vehicle by engaging the Telescoping Anti-Rotation System (TARS). The TARS must be aligned with the frame plate of the host vehicle to engage the anti-rotational arms and its bumper must be able to resist the anticipated TL 3 design impact loads to ensure optimal attenuator crash performance.
We initially agreed these modifications and attachment details were unlikely to affect the test results previously submitted for the Scorpion C 10,000 TMA for the two required TMA tests, i.e., tests 3-50 and 3-51. To verify the trailer's performance you conducted test 3-51M using a 10,000 pound host vehicle with trailer axle configurations in the middle and at the rear. A summary of these two 3-51M test results are enclosed. Test 3-51M is a modified version of the standard 3-51 test in which a 10,000 pound host vehicle was used instead of the standard 20,000 pound host vehicle. The center mounted axle configuration resulted in a more severe impact of 22.6 g's of ridedown acceleration that exceeded the maximum allowable 20 g's. Therefore, the trailer design was modified to replicate the original Scorpion C 10,000 TMA with a rear axle configuration and removal of a non-compressible center section. When impacted, the modified rear axle configuration design recorded a ridedown acceleration measuring the maximum allowable of 20 g's. The actual forward roll of the lighter host vehicle was determined to be between 60 and 70 feet when impacted by the 4,500 pound (2000P) test vehicle.
Additionally, you conducted optional tests 3-52 and 3-53 using the standard 20,000 pound host vehicle and the center mounted axle configuration to validate acceptable performance of an off-center impact. We had previously agreed that test 3-52 was a sufficient test when converting a TMA design to a trailer mounted attenuator, in line with the testing conducted by other manufacturers Your tests were conducted with the center mounted axle and the non-compressible center section. Based on the results of the optional tests, we agree that the added steel tongue trailer attachment with the TARS prevented the trailer attenuator from rotating in an offset, angled rear impact. The center axle configuration of the attenuator trailer as tested for 3-52 and 3-53 with non-compressible center section presented an equivalent or more severe impact than could be expected with the rear axle configuration and passed the testing criteria. The summary results of both optional tests are enclosed.
During our review we requested additional information which you provided We ultimately concluded that Test 3-51 should not be waived due to the design modifications made when converting your TMA to a trailer TMA Therefore on March 5, 2007, we requested that you conduct a Test 3-51 of your final Scorpion Trailer TMA using a standard weight host vehicle On March 9, 2007, this test was conducted by Karco with acceptable results, including a ridedown acceleration measuring 14.6 g's A summary of the Test 3-51 results are also enclosed for reference.
After reviewing the matrix of tests conducted and additional information you sent us, the FHWA acknowledges with the conditions that the Scorpion Trailer Attenuator with the rear mounted axle configuration and steel tongue TARS attached to host vehicles weighing 10,000 to 20,000 pounds meets the appropriate evaluation criteria under NCHRP Report 350 Tests 3-50, 3-51, 3-52, and 3-53 The Scorpion Trailer Attenuator may be used as a TL-3 TMA on the National Highway System when such use is acceptable to the contracting authority.
Please note also that the following provisions apply to the FHWA letters of acceptance:
John R. Baxter, P.E.
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