Oklahoma bridges are rated using the National Bridge Inventory (NBI) 0–9 rating scale.

Inspectors give a rating to each of the bridge’s primary elements: deck, superstructure, and substructure.

The National Bridge Inventory System (NBIS) requires each state highway department to inspect, prepare reports, and determine load ratings for bridges on all public roads.

Bridges or culverts that carry vehicular traffic and are longer than 20 feet are part of the NBIS or NBI. Bridges or culverts that do not carry vehicular traffic or are equal to or less than 20 feet are not part of the NBIS.

Structurally Deficient: If a bridge is structurally deficient it means there are elements of the bridge that need to be repaired or monitored. A bridge labeled structurally deficient is not necessarily unsafe; it means they must be maintained, inspected and monitored.

Most deficient bridges are left open to traffic during its maintenance and repair, and if inspectors find unsafe conditions they can close the bridge or restrict it to light vehicles with lowered speed limits.

Functionally obsolete: A bridge that is functionally obsolete is not necessarily unsafe, it just means the bridge has older design features not built to today’s standards. A functionally obsolete bridge is not wide enough or tall enough, so it cannot safely accommodate current vehicle sizes, weights and traffic volumes.

The sufficiency rating helps determine what bridges could need repair or replacement; it also affects the bridges eligibility for federal funding. Bridges must have a rating of 50 or below to qualify for federal replacement funds. The sufficiency rating must be 80 or below to get federal rehabilitation funding.

Oklahoma bridges are rated using the National Bridge Inventory, or NBI, 0–9 rating scale.
Inspectors give a rating to each of a bridge’s primary elements: deck, superstructure and substructure.

• Deck - The portion of the bridge that directly carries traffic.
• Superstructure - The portion of the bridge that supports the deck and connects one substructure element to another.
• Substructure - The portion of the bridge that supports the superstructure and distributes all bridge loads to below-ground bridge footings.

• 9 (Excellent)
• 8 (Very good) - no problems noted.
• 7 (Good) - some minor problems.
• 6 (Satisfactory) - structural elements show minor deterioration.
• 5 (Fair) - all primary structural elements are sound but may have minor corrosion, cracking or chipping. May include minor erosion on bridge piers.
• 4 (Poor) - advanced corrosion, deterioration, cracking or chipping. Also significant erosion of concrete bridge piers.
• 3 (Serious) - corrosion, deterioration, cracking and chipping, or erosion of concrete bridge piers have seriously affected deck, superstructure, or substructure. Local failures are possible.
• 2 (Critical) - advanced deterioration of deck, superstructure, or substructure. May have cracks in steel or concrete, or erosion may have removed substructure support. It may be necessary to close the bridge until corrective action is taken.
• 1 (“Imminent” failure) - major deterioration or corrosion in deck, superstructure, or substructure, or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to traffic but corrective action may put back in light service.
• 0 (Failed) - out of service - beyond corrective action.
• N (Not Applicable)