April 30, 2002

> Refer to: HSA-10/B99

Larry F. Sutherland

Deputy Director, Office of Roadway Engineering Services

Ohio Department of Transportation

P.O. Box 899

Columbus, Ohio 43216-0899

Dear Mr. Sutherland:

In your April 3 letter, you requested the Federal Highway
Administration's (FHWA) acceptance of the Ohio Department of
Transportation's Thrie-beam transition to a vertical concrete parapet as
a National Cooperative Highway Research Program (NCHRP) Report 350
transition design at test level 4 (TL-4). Mr. Powers independently
received copies of the Texas Transportation Institute (TTI) test reports
dated August 2001, entitled "NCHRP Report 350 Test 3-21 on the Ohio Type
1 Transition from Thrie Beam to Concrete Parapet with Asphalt Curb" and
February 2002, entitled "NCHRP Report 350 Test 4-22 on the Ohio Type 1
Transition from Thrie Beam to Concrete Parapet with Asphalt Curb" and
videotapes of the two tests that were conducted.

The tested transition design consists of 3810 mm of nested Thrie-beam
rail bolted to a vertical-faced concrete parapet at the bridge end and
connected to standard w-beam barrier with a 12-gauge symmetric w-beam to
Thrie-beam transition piece on the approach end. The first post was
approximately 1.26 m from the parapet and the second post 952.5 mm from
the first. Both posts were 2440-mm long W200 x 35.9 steel posts. The
next three posts were also on 952.5-mm centers, with post no. 3 being a
2440-mm long W150 x 37 and post nos. 4 and 5 being the same size, but
only 1830-mm long. Post no. 6 was the same size and length as posts 4
and 5, but with a 1905-mm spacing. All remaining posts were standard
strong posts on 1905-mm centers. All posts used routed wood offset
blocks. A 7.1-m long, 100-mm high and 152-mm wide asphalt curb was
installed with its traffic face 25 mm in front of the Thrie-beam.
Enclosure 1 shows these and other design details.

Tests 3-21 (pickup truck) and 4-22 (single unit truck) were conducted on
the Ohio transition design and the summary results are shown in
Enclosure 2. All evaluation criteria were met, although the passenger
compartment intrusion in the pickup truck was judged to be marginal. I
am aware that the same test, but without the asphalt curb, resulted in
unacceptable passenger compartment intrusion. Thus the 100-mm high curb
is an essential design element. This curb can be made of asphalt, as
tested, or it may be a concrete curb. You may wish to specify a curb
higher than 100 mm to reduce wheel snagging on the concrete parapet and
enhance overall crash performance. You should also consider specifying a
10-gauge w-beam to Thrie-beam transition piece in your design. Tests by
other agencies have shown that a 12-gauge piece is not stiff enough when
connected directly to nested Thrie-beam and can tear when struck at that
location.

Based on the reported test results, and subject to your consideration of
the above recommendations, I conclude that your Thrie-beam transition
design satisfies the evaluation criteria for an NCHRP Report 350 test
level 4 (TL-4) transition and may be used on the National Highway
System.

Sincerely yours,

(original signed by A. George Ostensen)

> A. George Ostensen

Program Manager, Safety

2 Enclosures