|
|
February 17, 2005
In Reply Refer To: HSA-10/CC-87
Mr. Barry D. Stephens, P.E.
Sr. Vice President Engineering
Energy Absorption Systems, Inc.
3617 Cincinnati Avenue
Rocklin, California 95678
Dear Mr. Stephens:
Your January 28, 2005, letter was recently delivered to Mr. Richard Powers of my staff by Mr. Douglas Bernard. In this letter, you requested formal Federal Highway Administration (FHWA) review and acceptance of a new crash cushion called the QUESTtm. To support this request, your letter also included a summary report prepared by E-Tech Testing Services that describes the QUEST and the eight full-scale crash tests that were conducted on this attenuator.
The QUEST is a redirective, non-gating crash cushion having an effective length of 5.74 m. It measures 610-mm wide at the backup and stands 813-mm tall. The mass of a fully assembled unit is approximately 600 kg. Its main components, as shown in Enclosure 1, include a ground-anchored backup assembly, two ground-anchored front anchors, two front rails, two rear rails, a nose, a trigger assembly, a sled, a diaphragm, a bridge, and panel assembles. The panels are fabricated from the American Association of State Highway and Transportation Officials' M-180 Class A (12 GA) w-beam. The nose and diaphragm sheet metal material and thickness designation is ASTM A 569 steel. All other flat bar or plate steel components are made from ASTM A36 steel. The fasteners and anchor/rail connections are specified as SAE J429 GD 8 and all others are SAE J429 GD 5. All components are galvanized per ASTM A123 to resist corrosion. The system can be preassembled and moved to the installation site or can be assemble on-site.
When the QUEST is impacted along the side, the sled, panels and rails go into tension and work together to steer the vehicle away from the hazard. A load-sharing component called the bridge is included in bay 2. The two front rails run the length of the system and are attached at one end to front anchors and at the other to a backup. These rails are supported off the ground at the sled, the diaphragm, and the bridge using guides (3 per side). The sled is secured to the front anchor using 12.7-mm diameter high-strength; all-threaded rods that pass through the front trigger assembly. During head-on impacts, the trigger mechanism is activated which releases the sled. Longitudinal collision energy is then dissipated though momentum transfer, though the re-shaping the front rails by shapers attached to the sled, though peeling of flat metal plates welded to the inside surface of the panels, and through a second set of shapers incorporated into the backup.
Since the QUEST is a completely new crash cushion, you conducted all eight certification tests recommended in the National Cooperative Highway Research Program (NCHRP) Report 350 for redirecting, non-gating crash cushions. These tests were conducted at test level 3 (TL-3) impact speeds (100 km/h). Tests included 3-30 through 3-33, and 3-36 through 3-39. Each test setup and results are described in your summary report and the one-page test summaries are shown in Enclosure 2. Most were conducted with the unit anchored to concrete, but Tests 3-37 and 3-39 were conducted with the unit anchored to asphalt. When anchored on concrete with a nominal compressive strength of 27.6 MPa., the foundation must be at least 150-mm thick (with reinforced concrete) or 203-mm thick (with no reinforcement). Thirty MP-3 anchors (19-mm diameter, B7, all-thread) with an embedment depth of 140 mm were used for the test series. When anchored to asphalt, the foundation must be at least 150-mm thick over 150-mm thick compacted sub-base and 38 of your MP-3 long-bolts (19-mm diameter, B7, all-thread) are specified with an embedment depth of at least 420 mm.
Tests 3-38 and 3-39 were conducted using a QUEST system equipped with an experimental nose that was later modified. I agree that the nose did not come into play during these two tests and later modifications to the nose would not compromise the results of these tests. I also recognize that the final nose and trigger configuration was validated in Test 3-37, which had an impact point very close to that in Test 3-38. I noted that Test 3-33 was conducted using a QUEST system that incorporated transition hardware to a downstream section of fixed CMB. This worst-case angular impact demonstrated the successful performance of the QUEST when attached to downstream transition hardware. The QUEST system is designed for installation at sites where bi-directional traffic is present. You submitted drawings (Enclosure 3) depicting transitions to w-beam and thrie-beam guardrail as well as New Jersey-shape and vertical concrete walls. I noted that these transitions are virtually identical to those validated in other testing programs previously accepted by the FHWA. Consequently, additional full-scale crash testing is not required for these QUEST transition designs, but, as with all safety hardware, informal field reviews or in-service evaluations are recommended to verify acceptable crash performance.
Your QUEST system meets the evaluation criteria for an NCHRP Report 350 redirective, non-gating crash cushion at TL-3 impact conditions and may be used on the National Highway System (NHS) when such use is acceptable to the contracting authority. The transition designs shown in Enclosure 3 are acceptable when the QUEST is connected to w-beam, thrie-beam, New Jersey- or vertically- faced CMB. Further the QUEST system can be anchored to concrete or asphalt surfaces if these surfaces duplicate the minimum anchoring foundations used in your testing program as noted above.
Please note also that the following provisions apply to the FHWA letters of acceptance:
Sincerely yours,
/Original Signed by Harry W. Taylor/
~for~
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety
