The Michigan Department of Transportation (MDOT) has once again updated information on the MDOT Web site at www.michigan.gov/highwaybridgereport about the safety of 4,401 state highway bridges.

MDOT has posted bridge safety reports online since August 2007. State bridge information can be downloaded by route number and/or county, and are current as of July 31, 2010. Only highway bridges greater than 20 feet in length are included; ratings for pedestrian, railroad and locally owned bridges are not included. MDOT is updating bridge condition information on the Web four times a year.

"Funding for bridge maintenance is being threatened by limited funding, but we remain committed to keeping state-owned bridges safe for travel," said State Transportation Director Kirk T. Steudle. "We are working year-round to monitor the condition of highway bridges to make sure they are safe for Michigan motorists."

National Bridge Inspection Standards require MDOT to inspect bridges every two years. The Mackinac, International, and Blue Water bridges are inspected annually, exceeding federal requirements. These three bridges are managed by bridge authorities, and their ratings are not included in the list MDOT has posted to the Web.

MDOT employs more than 20 bridge inspectors who have specialized training and work in teams of two. Bridge inspectors use a variety of tools to assess bridge safety and structural integrity. The types of inspection performed include bridge safety inspections, fracture critical inspections, fatigue-sensitive inspections and underwater inspections. Non-destructive evaluation and bridge monitoring also is done as needed. Techniques used include calipers to measure the thickness of steel, ultrasonic testing to check for defects in steel, sounding to detect concrete separation, and monitoring bridge deflections and response to load.

Of the 4,401 bridges on the July 31, 2010, report, 429 are classified with the engineering term of "structurally deficient," meaning they may require rehabilitation or replacement at some time in the future; and 883 bridges are classified as "functionally obsolete," meaning they are outdated and may require modernization at some time in the future. The report lists six more structurally deficient bridges and 18 less functionally obsolete bridges in July than it did in March.