September 5, 2002
Mr. Rodney A. Boyd
Trinity Highway Safety Products Division
Dallas, Texas 75356-9619
Dear Mr. Boyd:
In his August 15 letter to Mr. Richard Powers of my staff, your consultant, James Albritton, requested the Federal highway Administration's (FHWA) review and acceptance of modifications to your TRACC and FASTRACC crash cushions. These modifications consisted of flared extensions to the original designs, thus making them suitable to shield wider hazards. To support this request, he also sent a Texas Transportation Institute report, dated August 2002, entitled “NCHRP Report 350 Testing and Evaluation of the WideTRACC” and videotapes of the tests that were conducted.
The WideTRACC is essentially a modification of the original 6.4-m long TRACC crash cushion. Approximately 2.9 m from the nose, the side panels, connected to four progressively wider support frames, begin to flare outward at a seven-degree angle. Depending on the width and location of the shielded object, either one or both sides of the TRACC can be flared. The wider frames are anchored to the asphalt or concrete foundation with special low-profile anchors, and the side panels are bolted to the widened frames with special joint plates that establish the seven-degree flare angle between the frames and the panels. At this point, the WideTRACC is 1.47-m wide at the rear. If the shielded object is wider than 1.47 m, the seven-degree flare can be continued in 0.71 m increments. Each added increment of length adds 0.17 m to the width of the system. As an example (assuming both sides are flared), a 3.56 m extension would result in a rear width of 2.34 m and the WideTRACC unit would be 9.94-m long. The extended sections are comprised of two 10-gauge W-beam panels bolted to W150 x 13 steel posts that have C75 x 6 channel braces behind each post. The posts and braces are welded to a common base plate that is bolted to the foundation. When the extension transitions to a rigid concrete wall, a C200 x 17 steel channel must be used between the lower W-beam and the braced support posts. These and other design details are shown in Enclosure 1.
Because the original TRACC was subjected to a full array of tests, only those tests likely to be affected by the flared sides of the WideTRACC were conducted. These included NCHRP Report 350 test 3-31 and test 3-38. The latter test was run twice. The first impact point was approximately at the point where the side panels began to flare and the second was at the transition point to a concrete safety shape barrier.
Summary reports for these three tests are shown in Enclosure 2.
Based on the information you provided, I agree that the WideTRACC, as described above and as shown in Enclosure 2, may be considered a test level 3 crash cushion and used on the National Highway System (NHS) when its use is acceptable to the contracting agency. Since it is a proprietary device, the conditions listed in Title 23, Code of Federal Regulations, Section 635.411 apply to its use on Federal-aid projects, except exempt, non-NHS projects.
I also agree that the wider design can be applied to your FASTRACC attenuator, which met NCHRP Report 350 evaluation criteria for test 3-31 (head-on impact with the 2000-kg pickup truck) at an impact speed of 112.3 km/h. When applied to the FASTRACC, the flared panels begin at the same location relative to the nose of the attenuator, but five progressively wider support frames must be used in advance of any transition section. Since only test 3-31 was run at the higher impact speed, there is no assurance that either version of the FASTRACC will meet NCHRP Report 350 evaluation criteria for a test level 3 (TL-3) attenuator at impact speeds greater than 100 km/h for any of the other impact conditions included in the Report 350 test matrix for crash cushions.
(original signed by Carol H. Jacoby)
Carol H. Jacoby, P.E.
Director, Office of Safety Design