Characteristics of Decommissioned Bridges Final Report

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The main objective of this research was to identify the main reasons for bridge decommissioning in the United States. Relevant studies from the literature reported deficiency, poor NBI condition ratings, lower load carrying capacities, vulnerabilities, and road widening projects as most common causes of bridge decommissioning. A common finding in the earlier studies was that reasons for decommissioning could not be identified for a significant portion (15% to 30%) of the records. For the first analysis in this research, decommissioned structures were identified from historic NBI files and their characteristics were analyzed. Based on a national survey performed for the project, the literature review, and initial analysis, potential drivers of decommissioning were then identified. These potential drivers were then compared with agency reasons gathered from five States (Utah, Michigan, California, Pennsylvania, and Florida). The final task was a comparative analysis of the decommissioned structures with the new structures that replaced them. Overall, functional improvements are the major driver of bridge decommissioning and they also explain majority of unexplained cases. Structures replaced due to functional reasons are also replaced younger than the structures replaced due to poor condition on average. Although the potential drivers provide sufficient identifiers of decommissioning, drivers derived from the NBI data by themselves are not specific enough to explain decommissioning as comprehensively as agency-provided reasons.


Mechanical and Civil Engineering