The Michigan Department of Transportation has once again updated information on the MDOT Web site at about the safety of 4,397 state highway bridges. At www.michigan.gov/highwaybridgereport, a variety of information is posted.
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 Oct. 1, 2011. 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.
“MDOT continues to make state highway bridge condition reports easily available to Michigan motorists on the MDOT Web site on a regular basis,” said State Transportation Director Kirk T. Steudle. “We are committed to monitoring and maintaining the safety of highway bridges and overpasses.”
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 4,397 bridges included in the Oct. 1 report, 341 are classified with the engineering term of “structurally deficient,” meaning they may require rehabilitation or replacement at some time in the future; and 899 are classified as “functionally obsolete,” meaning their design is outdated and may require modernization at some time in the future. Four bridges were removed and two were added. The report lists 37 fewer structurally deficient bridges and 56 more functionally obsolete bridges in October than in May 2011.