Beyond State-Level Bridge Counts--Alternative Performance Measures for Evaluating Bridge Conditions

After the catastrophic collapse of the I-35W Bridge in Minneapolis, MN in August 2007, bridge conditions came under increased scrutiny. Legislative discussions focused heavily on the need for more frequent bridge inspections and more federal funding to rehabilitate and replace the nation’s worst bridges. Unfortunately, the extent of these public discussions has been largely at an aggregate level (nationwide or statewide) and often only considers the number of deficient bridges in any geographic area. Using historical data from the National Bridge Inventory, this paper looks at deficient bridges between 1992 and 2008. Beyond simply considering the number of deficient bridges, the paper looks at trends in deficient bridge deck area, a relative measure of size. Further, the paper looks at trends in deficient bridges at different geographic levels including nationwide, statewide and within metropolitan areas. Two case studies are presented (Baltimore, MD and Seattle, WA) to highlight some of the longitudinal trends that can be observed at the metro level using different bridge measures. The results of the analysis suggest that bridge needs are increasingly concentrated in metropolitan areas, and that the average deficient bridge is increasing in size. The paper concludes with a brief discussion of future research needs.