Report Result

Back to Search

Development of an Approach Guardrail Transition Attached to a Thrie Beam and Channel Bridge Railing

REPORT NUMBER

TRP-03-091-99

AUTHORS

Karla Lechtenberg (Polivka), Ronald Faller, John Reid, Dean Sicking, John Rohde, Eric Keller, James Holloway

PUBLICATION DATE

2000-03-21

ABSTRACT

An approach guardrail transition was developed for use with Missouri's thrie beam and channel bridge railing system. Two 2000-kg pickup truck crash tests were performed unsuccessfully on two previous designs according to the requirements specified in NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. In both instances, the pickup truck rolled over upon redirection. For those two prior designs, a rubrail was used below the thrie beam guardrail in the transition region to prevent wheel snagging on the first bridge post; since, the bridge railing system did not incorporate post blockouts. The inclusion of the rubrail in the design was believed to have greatly influenced the angular motions of the vehicles during both impacts. Upon reviewing the crash test results, it was deemed necessary to modify the bridge railing system to incorporate spacers in order to position the thrie beam away from the face of the bridge posts. This change would allow the rubrail to be completely removed as the potential for wheel snagging would be essentially eliminated. After Missouri approved the use of spacer blocks, it became apparent that an existing NCHRP350 TL-4 transition design could be modified slightly and easily adapted for use with Missouri's bridge railing system. The TL-4 transition design was initially developed for the Forest Products Laboratory of the U.S. Forest Service. A modified transition detail was prepared for use with Missouri's bridge railing system, and a request was sent to the Federal Highway Administration (FHWA) seeking approval of this new design without additional crash testing. Subsequently, the transition system was approved for use by FHWA as a TL-3 transition system contingent upon the inclusion of spacer blocks in the bridge railing system.