August 29, 2003
Mr. Daniel J. Mushett
Interstate Timber Products Co.
111 Garnet Lane
Oak Ridge, Tennessee 37830
Dear Mr. Mushett:
Your recycled plastic offset block (P-Block) for use with strong steel post w-beam guardrail was accepted for use on the National Highway System (NHS) on November 7, 2002, (Federal Highway Administration (FHWA)) acceptance letter B109).
In your July 11, 2003, letter to Mr. Richard Powers of my staff you requested acceptance of a similar offset block for use with round wood posts, an alternative strong post w-beam guardrail system used by some State Departments of Transportation. You indicated that the modified block (PC-Block) is comprised of the same materials as the P-Block (50/48 blend of High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) with 2 per cent blowing agent), but has modified dimensions to fit the round wood post. Specifically, the traffic face remains 4-inches wide and its effective depth has been retained at 7.65 inches, but the field side of the block has an approximate 3.5-inch radius to fit against the standard 7-inch diameter round wood posts. These details are shown on the enclosed drawing.
I agree that this block is acceptable for use with strong, round post w-beam guardrail installations on the NHS. Please note the following standard provisions that 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