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 4,408 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 March 30. 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.
“The state is committed to ensuring that these structures remain safe,” said State Transportation Director Kirk T. Steudle. “Posting highway bridge condition reports online keeps us accountable to the motoring public and fits with Gov. Snyder’s goal of keeping government transparent.”
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 4,408 bridges included in the March 30, 2012, report, 287 are classified with the engineering term of “structurally deficient,” meaning they may require rehabilitation or replacement at some time in the future; and 1,070 are classified as “functionally obsolete,” meaning their design is outdated and may require modernization at some time in the future. The Nettle Run bridge on M-142 in the Thumb region of the state was the only bridge added to the list as of March 30. The last highway bridge report was posted to the Web on Jan. 23, 2012, and covered bridge inspections through Dec. 29, 2011. The new report lists 12 fewer structurally deficient bridges and 93 more functionally obsolete bridges than on Dec 29, 2011.
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