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ABSTRACT

Full-scale 4,500 lb. vehicle impact tests at 60 mph and 25 deg. were conducted on four new guardrail-bridgerail "transition" designs for use in Nebraska in which the first wood post from the bridge end was left out. The post was left out to represent a common field problem in which a concrete footing prevents the installation of the post. To compensate for the post left out, a stronger beam member and heavier wood posts were used in addition to a 4:1 tapered-end on the end of the concrete bridgerail. The tapered-end was used to (1) reduced the unsupported span length, and (2) provide a smooth guardrail deflection curve during vehicle redirection. All of the transition designs were identical except for the transition beam member. The designs consisted of 2 heavy 10 in. x 10 in. posts followed by 4 heavy 8 in. x 8 in. posts. The remaining posts were standard 6 in. x 8 in. posts. Over a guardrail length of 18 ft.-9 in., the posts were spaced 3 ft.-1 1/2 in. centers, whereas, over the remaining length, a standard post spacing of 6 ft.-3 in. was used. The posts were installed in a "native" silty-clay (type CL) soil. In terms of the evaluation guidelines in NCHRP 230, the overall performance of the transition designs were: Single Thrie Beam Transition: Unsatisfactory Double Thrie Beam Transition: Satisfactory Tubular Thrie Beam Transition: Satisfactory Double W-Beam Transition: Unsatisfactory

KEYWORDS

Guardrail Transitions, Crash Tests, Roadside Safety

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