Date of Award

Fall 2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Andrew Tarko

Committee Chair

Andrew Tarko

Committee Member 1

Hao Zhang

Committee Member 2

Fred Mannering

Committee Member 3

Samuel Labi

Abstract

Road barriers have been used as an effective countermeasure to prevent exposure of errant vehicles to vehicles travelling from the opposite direction or roadside hazards. The objective of this study is to evaluate the in-service safety performance of three types of road barriers (concrete barriers, W-beam guardrails, and high-tension cable barriers) in Indiana using cross-sectional statistical analysis. The evaluation was comprised of three components: 1) the effect on the crash frequency (segment level), 2) the effect on the probabilities of hazardous events (crash level), and 3) the effect on the probabilities of injury outcomes (occupant level). Crash costs, as a measure of overall safety performance, were finally estimated for each studied barrier and non-barrier scenario.^ This study found that both the median and roadside barriers were effective in reducing crash costs, and that the former was the more effective of the two. Their main benefits were the reduction of cross-median head-on events for median barriers and reduction of non-cross-median high-risk events (rollover or hitting a sturdy roadside object) for roadside barriers. Crash costs were roughly cut in half with either the use of cable barriers in wide medians (median width larger than 50 feet) or the use of concrete barriers and guardrails in narrow medians (median width less than or equal to 50 feet). The use of a roadside guardrail resulted in roughly 20% to 30% crash cost reduction. ^ Median cable barriers were found to be most effective among all the studied barriers due to their smaller increase in crash frequency and less of the severe injury outcomes associated with cable barrier collisions. A cable barrier's offset to the roadway was also investigated in this study. Nearside cable barriers (offset less than or equal to 30 feet) were shown to perform better than far-side cable barriers (offset larger than 30 feet) due to the former's larger reduction in non-cross-median high-risk events such as vehicle rollovers in the median. The findings of this study can help agencies develop: (1) criteria that justify consideration of road barriers, (2) guidelines for selecting the barrier type and related characteristics, and (3) crash cost modification factors to facilitate the cost-effectiveness analysis.

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