Drivers of Bridge Decommissioning in the United States

Extending the useful life of bridges through better design, construction, and management is a shared effort among the bridge management community. Data in the National Bridge Inventory (NBI) is valuable for understanding the behavior of bridges throughout their service lives. While the primary reason for bridge replacement, intuitively, would be condition, research has indicated that bridge replacement may not necessarily be driven by the condition of the bridge. The estimated median service life for bridges, 53 years, is much lower than the desired service life of 75 years. This paper summarizes the results of an NCHRP Project which identified the main drivers for bridge decommissioning in the United States, based on findings from three complementary analyses using historic NBI data files, select agency records, and data from old and new structure pairs. A common finding in previous studies was that a significant portion (15–30%) of decommissioning could not be associated with any particular reason. Although poor condition is a significant factor, the major driver of bridge decommissioning is functional improvement, and this explains the majority of the unexplained cases. Structures replaced due to functional reasons tend to be replaced at a younger age, leading to a decrease in the overall decommissioning age. While decisions on functional improvement projects are not led by bridge offices, bridge networks are substantially affected by these decisions. Coordinating functional improvement decisions at the agency level and integrating relevant information with decision support tools can improve financial planning and asset management processes.