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 4,422 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 Aug. 30, 2013. 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.
“While limited funding remains a challenge, MDOT is committed to monitoring highway bridges and maintaining the safety of highway bridges and overpasses,” said State Transportation Director Kirk T. Steudle. “We’ve been putting this information online for six years now because transparency and accountability are important to us and the citizens we serve.”
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 4,422 bridges included in the Aug. 30, 2013, report, 269 are classified with the engineering term of “structurally deficient,” meaning they may require rehabilitation or replacement at some time in the future; and 828 are classified as “functionally obsolete,” meaning their design is outdated and may require modernization at some time in the future. Five bridges were removed and four were added. The last highway bridge report posted to the Web covered bridge inspections through April 24, 2013. The new report lists 77 fewer functionally obsolete bridges and 20 more structurally deficient bridges than on April 24, 2013.
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