March 17, 2005
Refer to: HSA-10/CC-89
Dean C. Alberson, Ph.D., P.E.
Associate Research Engineer
Texas Transportation Institute
College Station, Texas 77843-3135
Dear Dr. Alberson:
In your February 26, 2005, letter, you requested the Federal Highway Administration's acceptance of a new reusable, redirective crash cushion called the Hybrid Energy Absorbing Reusable Terminal (HEART) at the National Cooperative Highway Research Program (NCHRP) Report 350 test level 3 (TL-3). To support your request, you also sent copies of a Texas Transportation Institute report dated January 2004, entitled "Testing and Evaluation of the HEART Crash Cushion," and videotapes of three crash tests you conducted on the new design. After initial staff review of the reported tests, we requested two additional tests, the results of which were sent to me on March 3 with a second Texas Transportation Institute report dated March 2005, entitled "NCHRP Report 350 Tests 3-33 and 3-37 of the HEART".
The HEART attenuator consists of three deformed (hinged) High Molecular Weight/High Density Polyethylene (HMW/HDPE) panels along each side connected to steel diaphragms mounted on tubular steel tracks. The assembled unit is approximately 26-feet long, 32-inches high, 25-inches wide at the diaphragms with a maximum width of 39 inches between diaphragms 3 and 4. The front anchorage consists of a W8 x 13 upper release post mounted to a 1/2-inch thick base plate. There are two slots at the slip plane between the upper and lower post through which tensioning cables are anchored. When the upper release post is impacted, the tensioned cables connected to diaphragm 2 are released and the side panels and steel diaphragms are pushed rearward along the base track. This track consists of a pair of 2 inch x 5 inch x 1/4 inch structural tubes stitch-welded above two C3 x 4.1 standard channels. The channels serve as spacers allowing the diaphragms to move longitudinally along the structural tubing during frontal impacts. Anchor bolts, ¾-inch diameter x 11-inches long, are placed through the structural tubing and channel at locations that can be accessed without removal of the plastic side panels or diaphragms and into 8-inch thick non-reinforced concrete. The rear backup structure is an 8 inch x 12 inch x ½ inch structural tube welded to a ¾-inch thick base plate. The last diaphragm (#10) is bolted to the structural tube. A second set of tensioning cables, attached to diaphragm 2, terminate on the rear side of diaphragm #10. Enclosure 1 shows the general layout of the unit and selected components.
Based on staff review of the results of the five NCHRP Report 350 tests that were conducted (and summarized in Enclosure 2), I agree that the HEART attenuator, as described above, meets the appropriate evaluation criteria for a TL-3 crash cushion. Since no transition design has yet been developed for a reverse direction hit and Report 350 Test 3-39 was not conducted, the HEART should not be used in locations where opposite-direction impacts are probable without further development and testing. However, the HEART may be used at all appropriate locations on the National Highway System when selected by the contracting authority, subject to the provisions of Title 23, Code of Federal Regulations, Section 635.411 as they pertain to proprietary products.
Safety Home | FHWA Home | Feedback