How Bridges Are Inspected: The NBI Process

Every two years, a trained engineer walks, climbs, and sometimes rappels across each of America's 624,191 public bridges. They are looking for cracks, corrosion, scour, settlement, and dozens of other signs that a bridge may be deteriorating. This process -- the National Bridge Inspection Program -- has been federally mandated since 1971, following the collapse of the Silver Bridge in Point Pleasant, West Virginia in 1967 that killed 46 people.

Bridge inspections are performed by state DOT employees, consultants, or local agency staff -- but they must meet federal qualifications. The FHWA requires that every inspection team leader be a licensed Professional Engineer (PE) or have completed a comprehensive bridge inspection training course and have a minimum of five years of bridge inspection experience. Many states have additional requirements.

The NBI recognizes several types of inspections:

• Routine Inspection: A hands-on, close-up inspection performed at least every 24 months. This is the standard inspection that generates the 0-9 condition ratings.
• Underwater Inspection: For bridges over water, divers inspect substructure elements below the waterline at least every 60 months.
• Fracture-Critical Inspection: Bridges with non-redundant steel members that could cause collapse if they failed receive special hands-on inspections at least every 24 months.
• In-Depth Inspection: A more detailed evaluation when a routine inspection reveals potential problems. May include load testing, material sampling, or non-destructive testing.
• Damage Inspection: Performed after a specific event (flood, earthquake, vehicle impact) that may have damaged the bridge.

Each routine inspection evaluates over 100 data fields for each bridge, but the core assessment focuses on three components:

1. Deck condition: Cracking, spalling, potholes, delamination, wearing surface deterioration, drainage, and expansion joint condition. 2. Superstructure condition: Section loss, cracking, deflection, bearing condition, paint/coating deterioration, and connection integrity. 3. Substructure condition: Settlement, erosion, scour, cracking, spalling, and structural movement at piers and abutments.

Each component receives a rating from 0 (failed) to 9 (excellent). For a complete explanation of the scale, see our [condition ratings guide](/blog/bridge-condition-ratings-guide).

After each inspection, the data is submitted to the state's bridge management system, which transmits it to the FHWA's National Bridge Inventory. The NBI is updated annually and contains records for every public bridge in the country with a span of 20 feet or more. This is the dataset that powers BridgeStats -- we analyze the raw NBI data and present it in an accessible format.

Every bridge profile on our site includes the full inspection history, so you can see how a bridge's condition has changed over time. [Search for any bridge](/search) to see its complete record, or browse by [state](/reports) to see how your state's bridges are doing.