September 5, 2002
Mr. Rich Peter, Chief
Roadside Safety Technology Branch
Materials Engineering and Testing Services
5600 Folsom Boulevard
Sacramento, CA 95819-4612
Dear Mr. Peter:
In your July 9 letter to Mr. Frederick G. Wright, former Program Manager for FHWA's Office of Highway Safety, you requested formal acceptance of a Thrie-beam bridge rail transition design that you developed and tested to NCHRP Report 350 test level 4 (TL-4). You noted in your letter that local FHWA acceptance had been granted and included copies of your May 2002 test report “Vehicular Crash Tests of a Nested Thrie-Beam Transition Barrier and crash test videotapes.
The final design consisted of a standard 4130-mm long section of nested Thrie-beam on the traffic side and a single section of Thrie-beam on the field side of the transition. One of the traffic side nested rails was 10-gauge. The other nested rail and the backside rail were both 12-gauge material. A 10-gauge transition piece was used between the Thrie-beam and the approach W-beam guardrail, and the next 2211-mm long section of W-beam was also 10-gauge material. Six 250 mm x 250 mm wood posts on 953-mm centers were used to support the transition. The five posts nearest the vertical concrete parapet (with a 125-mm chamfer on its leading edge) were 2440-mm long. The sixth large post, at the W-beam to transition piece location, was 1830-mm long. These details are shown in the enclosure.
Three tests were successfully conducted on this design: the 2000-kg pickup truck impacting at a nominal speed of 100 km/h and at 25 degrees with the vehicle centered on the concrete parapet and again with it impacting just upstream from the W-beam to Thrie-beam transition piece, and the 8000-kg single unit truck impacting at 75.5 km/h and 16 degrees approximately 2 m from the concrete parapet.
Based on staff review of the information you provided, I agree that the transition described above meets all evaluation criteria for an NCHRP Report 350 bridge rail transition at test level 4 (TL-4) and it may be used on the National Highway System. Since it is a non-patented design, I assume that any agency interested in detailed drawings or test results may contact you directly at email@example.com or by telephone at (916) 227-7257.
(original signed by Carol H. Jacoby)
Carol H. Jacoby, P.E.
Director, Office of Safety Design