How to read bridge entries:
Example entry: Minnesota Highway 1 over Kawishiwi River | 4-6-7 | 46.3 | Built in 1936 | 530 cars per day | Fracture critical | Under construction
The three numbers (4-6-7 above) rate various aspects of the bridge. These are determined on a scale of 0-9, with 9 being excellent. A rating of 4 in any category means the bridge is structurally deficient. The first number rates the deck, the portion of the bridge vehicles ride on. The second number rates the superstructure, the portion that holds the deck up. The third number rates the substructure, the base of the structure that holds up both the superstructure and the deck.
The percentage figure (46.3 above) is the sufficiency score. A score of 80 percent or less means the bridge might need some work. A bridge with a sufficiency rating of 50 percent or less means the bridge may need to be replaced.
Note: The map does not include about five structurally deficient bridges in area forests.
The data is based on 2005 through 2007 inspection reports from the various city and county road agencies, the Minnesota Department of Transportation and Wisconsin Department of Transportation, and the National Bridge Inventory database. This map was compiled by Duluth News Tribune staffers Keith Faber and Jason Mohr, with research by Patrick Garmoe.