Bridge vs Dam: Understanding America's Infrastructure

The United States maintains two massive inventories of critical water-crossing infrastructure: 624,191 bridges tracked by the National Bridge Inventory (NBI) and approximately 72,949 dams tracked by the National Inventory of Dams (NID). Both face aging challenges, but the risks, inspection regimes, and funding mechanisms are quite different.

Bridges are inspected at least every 24 months under a mandatory federal program. Each bridge receives component ratings (0-9 scale) for its deck, superstructure, and substructure, plus an overall sufficiency rating (0-100). This standardized system makes it easy to compare bridges nationally. Learn more in our [condition ratings guide](/blog/bridge-condition-ratings-guide).

Dam inspections are less standardized. Federal dams are inspected by their owning agency (Army Corps of Engineers, Bureau of Reclamation, etc.), while state-regulated dams follow state-specific inspection schedules that vary widely. Dam condition assessments use categories (Satisfactory, Fair, Poor, Unsatisfactory) rather than numeric ratings.

The risk profiles of bridges and dams differ fundamentally. A bridge failure typically affects the people on or near the bridge at the time of failure. A dam failure can flood entire downstream valleys, potentially affecting thousands of people and causing catastrophic property damage. This is why 13,842 dams carry a "high hazard" classification. For details, see our article on [high hazard dams](/blog/high-hazard-dams-america).

Bridge failures, while less catastrophic in scope, are far more frequent. Every year, dozens of U.S. bridges experience partial or full failures due to age, scour, overloading, or impact damage. The 41,685 bridges currently in poor condition represent the highest-risk portion of the bridge inventory.

BridgeStats provides comprehensive data for both bridges and dams. Browse the [dam inventory by state](/dams), or explore [bridge conditions by state](/reports). For a deeper look at which states face the greatest bridge challenges, see our [state infrastructure rankings](/blog/best-bridge-infrastructure-by-state-2025).