Safety Investigation and Guidance for Retrofitting Existing Approach Guardrail Transitions
Eric Jowza, Ronald Faller, Scott Rosenbaugh, Dean Sicking, John Reid
A recent survey of approach guardrail transition systems in use along highways and roadways in the State of Wisconsin determined that a number of the transition systems were installed in a manner which deviated from the as-tested design details. These deviations included: missing transition posts; transition posts installed near or at slope break point of fill slope; insufficient soil backfill/grading behind transition posts; wood posts installed in asphalt surfacing; and the presence of drainage structures (i.e., flume) below the rail. These deviations in approach guardrail transition installations were examined using a combination of: prior research results; engineering experience; an extensive BARRIER VII computer simulation effort; and a total of eight dynamic component tests on wood and steel posts embedded in soil with varying terrain and/or foundation conditions. This investigation was performed to evaluate whether the noted design deviations degraded barrier performance for two commonly-used approach guardrail transition systems in the State of Wisconsin. When design deficiencies were determined based on computer simulations, dynamic component testing, and estimated critical limits, several design modifications were developed for use in retrofitting existing transition systems to resolve such deficiencies.
Highway Safety, Roadside Appurtenances, Approach Guardrail Transitions, Retrofitting Existing Systems