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Inspectors regularly assess the condition of bridges across the state. A review of Illinois Department of Transportation data showed that 400 out of 3,460 bridges in the six-county Chicago metro area are considered "structurally deficient," meaning they are in need of repair or possibly replacement. That's nearly 12 percent.

Problem bridges include heavily traveled spans like the Lake Shore Drive bridge over the Chicago River, which is just north of the stretch of the drive that closed Monday, and the I-80 bridges over the Des Plaines River in Joliet. Here are key measurements of metro Chicago bridges labeled by the state as structurally deficient.

For the bridge to be deemed deficient, inspectors must find that the deck, superstructure or substructure is in poor condition, with advanced deterioration and breakage in critical areas.

Structurally deficient bridges

The structural deficiency rating (0 to 100) combines condition of a bridge's deck and structure, how functional it is and how much it is used.

LEGEND May need to be replaced

May need to be replaced May need to be repaired

May need to be repaired Partially in poor condition Circles sized by average daily traffic. Larger circles indicate more traffic.