  |
 
|
January 13, 2004
Refer to: HSA-10/CC-54F
Mr. Rodney A. Boyd
Trinity Industries
2525 Stemmons Freeway
Dallas, Texas 75207
Dear Mr. Boyd:
In his December 11 letter to Mr. Richard Powers of my staff, your consultant Mr. James Albritton, requested Federal Highway Administration acceptance of specific design changes made to the original TRACC crash cushion. These changes were:
- The impact sled was changed from a single weldment to a six-piece bolt-up assembly. As seen in enclosure 1, the weight of the sled was reduced by eliminating the original four horizontal angle stiffeners and bolting the w-beam side panels directly to the impact sled frame using high-strength 5/8-inch bolts, with a 1/4-inch rectangular washer (2-1/4 x 3) under the head of each bolt on the outside of the panels and two rectangular washers between each panel and the frame acting as spacers. This connection will be part of the TRACC assembly done by Trinity prior to shipment.
- The original single-piece, heat-treated cutter plate in the impact sled was replaced with a pair of hardened steel bolts, backed by a steel plate welded to the sled assembly (enclosure 2). The leading edge of these bolts shear the rip plates when the front end of the TRACC is impacted and the sled is forced backwards.
- The 5-mm (3/16-inch) thick Stage 2 and Stage 3 rip plates were modified by adding 25.4-mm (one inch) diameter holes on 73-mm (2-7/8 inch) centers. The same size holes were added to the 10-gauge rip plates used in Stage 3, but on 68-mm (2-11/16 inch) centers. The 16-gauge rip plates used in Stage 1 were not modified and retained the same 2-1/2-inch long slots on 3-inch centers that were used in the original design.
To confirm that these design changes did not adversely affect crash performance, crash tests were conducted at the Texas Transportation Institute (TTI) and described in that agency's January 2004 reports entitled "NCHRP Report 350 Test 3-31 of the Modified TRACC" and "NCHRP Report 350 Test 3-32 of the Modified TRACC." Since changes to the impact sled should have no measurable effect on side-impact performance, tests 3-31 and 3-32 were selected as being the most critical and were conducted. The summary results of these two certification tests are shown as enclosures 3 and 4.
Based on staff review of the design changes and certification test results, I consider the modified TRACC design as described above and shown in the enclosures acceptable for use on the NHS as a substitute for all previously-accepted TRACC designs, including the ShorTRACC, FasTRACC (test 3-31 only), and WideTRACC, at the same test levels at which they were previously accepted.
Sincerely yours,
(original signed by John R. Baxter)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety
4 Enclosures
