The Michigan Department of Transportation (MDOT) has updated information on the MDOT Web site at www.michigan.gov/highwaybridgereport about the safety of 4,406 state highway bridges.
MDOT has posted bridge safety reports online since August 2007. State bridge informationcan be downloaded by route number and/or county, and is current as of June 29. 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.
“Monitoring the condition of state highway bridges and ensuring their safety is extremely important to MDOT,” said State Transportation Director Kirk T. Steudle. “Posting highway bridge condition reports online is more than a performance measurement for our department. It’s our way of keeping the public informed of steps we are taking to responsibly manage the state’s vital transportation assets.”
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 4,406 bridges included in the June 29, 2012, report, 279 are classified with the engineering term of “structurally deficient,” meaning they may require rehabilitation or replacement at some time in the future; and 852 are classified as “functionally obsolete,” meaning their design is outdated and may require modernization at some time in the future. The last highway bridge report was posted to the Web on April 17, 2012, and covered bridge inspections through March 30, 2011. The new report lists eight fewer structurally deficient bridges and 218 fewer functionally obsolete bridges than on March 30, 2011.