September 12, 2003
Mr. Randy L. Warner
Director, Product R&D
Stabler Companies, Incorporated
635 Lucknow Road
Harrisburg, Pennsylvania 17110-1635
Dear Mr. Warner:
Your August 27, 2003, letter to Mr. Michael S. Griffith, former Acting Director of the Office of Safety Design, requested formal Federal Highway Administration (FHWA) review and acceptance of a redirective, non-gating crash cushion called the Smart Cushion Innovations - 100GM (SCI-100GM). To support this request, you also sent copies of test reports prepared by KARCO Engineering detailing the results of the full-scale crash tests you conducted on your attenuator.
The SCI-100GM is a redirective, non-gating crash cushion, 6550 mm long and 850 mm high. Its main components, as shown in Enclosure 1, include base and side frame assemblies fabricated of mild steel tubing, a front sled assembly, and a series of 10-gauge galvanized Grade 50 steel side panels mounted to collapsing steel frames, and a shock arresting cylinder. A 1.125-inch diameter steel cable is attached to the front sled assembly and is then routed around a front sheave to dual sheave assemblies located at the back of the attenuator (one at either end of the shock arresting cylinder). The unit telescopes backward upon frontal impact and generates its stopping force from a combination of friction between the cable and the non-rotating sheaves, acceleration of the attenuator's masses, crush factors in the body and frame of the vehicle, and the variable resistance created by the shock arresting cylinder as it is compressed between the rear sheave assemblies by the tensioned cable. The shock arresting cylinder is metered to apply a variable resistive force to the cable in relation to the speed and mass of an impacting vehicle.
The base unit is anchored to the mounting substrate with 48 bolts. Testing was performed on a unit mounted on a concrete pad with galvanized Grade B7 all-thread rods 0.75-inches in diameter and seven inches long. These rods were inserted into .875-inch diameter holes and set with epoxy.
You conducted five certification tests (National Cooperative Highway Research Program ((NCHRP)) Report 350 tests 3-31, 3-32, 3-33, 3-37, and 3-39), the results of which are summarized in Enclosure 2. Test 3-30 was tentatively waived on the assumption that test 3-32 would be more demanding for the small car. A review of the test results for tests 3-31 and 3-33 verified that the occupant impact velocity was greater for the angle hit than for the head-on impact for the pickup truck. Thus, one can reasonably assume the same relationship would hold for the car and I agree that test 3-30 may be omitted from this test matrix. You also requested that tests 3-36 and 3-38 be waived. Given the stiffness of the SCI-100GM seen in tests 3-37 and 3-39, I can also agree that these tests be waived. I ask, however, that you conduct a two-year in-service evaluation of the SCI-100GM and report your findings to me to verify acceptable field performance. You stated in your transmittal letter that all certification tests were conducted on the same hardware and only one side panel and one bolt were replaced during the testing, thereby minimizing repair costs and time. Your in-service evaluation should also be an excellent means of verifying and documenting the re-usability of this crash cushion.
Your SCI-100GM meets the evaluation criteria for an NCHRP Report 350 redirective, non-gating crash cushion at test level 3 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 2 are acceptable when the SCI-100GM is connected to a solid concrete barrier or backup. When attached to w-beam or Thrie-beam median barrier, that barrier must include an acceptable transition design, i.e., one accepted for use as a bridge rail transition, to redirect vehicles impacting from the backside and to prevent their snagging on the back corner of the attenuator. Acceptable transition designs require nested w-beam and a rubrail or nested Thrie-beam, as well as a post size and layout comparable to a currently acceptable bridge rail transition. Specific details can be found under Longitudinal Barriers, key word: Bridgerail Transitions on our safety hardware website at http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/.
Please note also that the following provisions apply to FHWA letters of acceptance:
(original signed by John R. Baxter)
John R. Baxter, P.E.
Director, Office of Safety Design
Office of Safety