Inspection Frequency

What It Means

Inspection frequency is the interval between required routine bridge inspections under the National Bridge Inspection Standards (23 CFR 650 Subpart C). The historical standard since 1971 has been a maximum 24-month interval for every bridge longer than 20 feet on a public road, with shorter intervals required for bridges in Poor condition or with critical findings. The 2022 NBIS revision introduced a formal risk-based inspection framework allowing intervals to range from 12 months (for bridges with serious deterioration, scour critical status, or other risk factors) up to 48 months (for bridges in Good condition with low-risk attributes and a robust inspection history). Specific inspection types have distinct frequencies: routine inspections (12-48 months depending on risk), in-depth inspections (as needed, focused on specific elements), fracture critical inspections (maximum 24 months, hands-on), underwater inspections (maximum 60 months for most bridges, shorter for scour critical or deteriorated substructures), and complex feature inspections (for cable-supported bridges, movable bridges, and similar specialized structures). The frequency is recorded in NBI Item 91 (Designated Inspection Frequency) and the date of most recent inspection in Item 90. When a state does not meet federal inspection frequency requirements, FHWA can withhold federal-aid apportionments. The 2022 revision responds to industry demand for more risk-based resource allocation, some bridges in excellent condition on stable foundations with low traffic genuinely do not change measurably over 24 months, while others in Poor condition with deterioration trajectories need more frequent monitoring. FHWA's Bridge Program Office publishes implementation guidance and maintains state-level compliance monitoring.

Frequently Asked Questions