Institute for Transportation

About the research

The 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 National Bridge Inventory (NBI) condition ratings, lower load-carrying capacities, vulnerabilities, and road widening projects as the most common causes of bridge decommissioning. A common finding in earlier studies was that the 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, a literature review, and an initial analysis, potential drivers of decommissioning were 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 a majority of unexplained cases. Structures replaced for 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.