December 2, 2009 -- State Transportation Director Kirk T. Steudle today announced that 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 4,398 state highway bridges. MDOT began making this information available to the public in August 2007.
This is the sixth time MDOT has made bridge safety information available on the Web. State bridge information can be downloaded by route number and/or county, and are current as of Oct. 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 making updates on the Web four times a year.
"We were one of the first DOTs to make information about state-owned highway bridges available to the public," said Steudle. "Citizens can be confident that state-owned highway bridges are safe, carefully inspected and well maintained."
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.
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 separation of concrete and monitoring bridge deflections and response to load.
Of the 4,398 bridges listed in the Oct. 30 report, 435 bridges are classified with the engineering term of "structurally deficient," meaning they may require rehabilitation or replacement at some time in the future; and 878 bridges are classified as "functionally obsolete," meaning they are outdated and may require modernization at some time in the future. The department is reporting 19 fewer structurally deficient bridges and seven fewer functionally obsolete bridges in October than it did in July. Since the July report, three new bridges were added to the list, and three bridges were removed from the list.
MDOT says: Remember - in Ice and Snow, Take it Slow!
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