How often are bridges inspected?

Federal law requires routine inspections of all public highway bridges every 24 months. Some bridges with known issues or unusual designs require annual or even more frequent inspections. Underwater inspections of submerged foundations are required every 60 months.

Who inspects bridges?

Bridge inspections are performed by qualified engineers or trained technicians who meet FHWA certification requirements under the National Bridge Inspection Standards. Most inspectors hold Professional Engineer licenses and have completed specialized bridge inspection training.

What do bridge inspectors look for?

Inspectors evaluate three main components: the deck (driving surface), superstructure (beams and trusses), and substructure (piers and abutments). They also check for scour, fatigue cracking, corrosion, settlement, and any signs of movement or distress.

What happens if a bridge fails inspection?

A bridge does not pass or fail in the traditional sense. Instead, each component receives a 0-9 rating. Bridges rated 4 or below on any component are classified as structurally deficient and may receive weight restrictions, increased inspection frequency, or be scheduled for repair or replacement.

How Bridge Inspections Work: A Complete Guide to FHWA Standards

The National Bridge Inspection Standards

The National Bridge Inspection Standards (NBIS) were established after the 1967 collapse of the Silver Bridge in Point Pleasant, West Virginia, which killed 46 people. That disaster revealed that the nation had no systematic program for monitoring bridge conditions. Congress responded by requiring regular inspections of all bridges on public roads longer than 20 feet.

Today, the NBIS governs inspection frequency, inspector qualifications, rating procedures, and reporting requirements. Every state must maintain an inventory of its bridges and submit condition data to the FHWA annually, creating the National Bridge Inventory database that BridgeSafety uses for its analysis.

Types of Bridge Inspections

The FHWA defines several types of inspections, each serving a different purpose:

Routine inspections — The standard inspection performed every 24 months. Inspectors visually examine all accessible parts of the bridge and assign condition ratings. This is the most common type and generates the data in the NBI.
In-depth inspections — More detailed examinations of specific components, often involving close-up access using snooper trucks, scaffolding, or rappelling equipment. These are triggered when routine inspections identify areas of concern.
Fracture-critical inspections — Specialized inspections of fracture-critical members, steel components whose failure could cause partial or total bridge collapse. Required at least every 24 months using hands-on, arms-length techniques.
Underwater inspections — Dive teams inspect foundations, piers, and other submerged structural elements. Required every 60 months for bridges over waterways.
Damage inspections — Unscheduled inspections triggered by events like floods, earthquakes, vehicle impacts, or other incidents that could damage the bridge.

The 0-9 Rating Scale

Inspectors rate three primary bridge components on a 0-9 scale defined by the FHWA Recording and Coding Guide:

Rating	Condition	Description
9	Excellent	New condition, no noteworthy deficiencies
8	Very Good	No problems noted
7	Good	Minor problems, some maintenance needed
6	Satisfactory	Structural elements show minor deterioration
5	Fair	All primary elements are sound but show minor cracks or spalling
4	Poor	Advanced deterioration, structural elements still function
3	Serious	Seriously affected section loss, deterioration, or scour
2	Critical	Critical condition, may need to close
1	Imminent Failure	Major deterioration, bridge may be closed
0	Failed	Bridge closed, beyond corrective action

BridgeSafety converts these numeric ratings into letter grades (A-F) using a weighted composite of the deck, superstructure, and substructure scores, with an age adjustment for bridges over 50 years old.

What Inspectors Actually Do on Site

A routine bridge inspection typically takes 2-8 hours depending on the bridge size and complexity. The inspector arrives with measuring equipment, cameras, hammers for sounding concrete, and detailed records from the previous inspection. They systematically examine:

Deck — The driving surface is checked for cracking, spalling, potholes, delamination, exposed rebar, and drainage problems. Inspectors may use chain-drag techniques to detect subsurface delamination not visible from the top.
Superstructure — Beams, girders, trusses, and other load-carrying members are examined for corrosion, fatigue cracks, section loss, buckling, and connection deterioration.
Substructure — Piers, abutments, and foundations are checked for settlement, tilting, cracking, scour, and erosion. Scour assessment is particularly critical for bridges over water.
Bearings and joints — Expansion joints and bearing pads allow the bridge to move with temperature changes. Seized bearings or failed joints can transfer unexpected forces to structural elements.
Approaches and guardrails — The road leading onto the bridge and all safety barriers are evaluated for condition and adequacy.

After the Inspection

Inspection findings are recorded in a standardized format and submitted to the state DOT, which forwards the data to the FHWA for inclusion in the National Bridge Inventory. If the inspector identifies a condition that poses an immediate safety concern, the bridge owner is notified immediately and may restrict traffic or close the bridge. For less urgent findings, the data feeds into the state's bridge management system for prioritization of repairs and funding.