Transportation officials failed to inspect some bridges, looked at deteriorating bridges less often than required by state law and did not check for erosion under bridges over rivers, Michigan's auditor said Friday.

The more than 10,000 bridges owned by the state and local governments must be inspected at least every two years.

An audit released Friday said more than 1,000, or 10 percent, of routine bridge inspections were not completed on time from October 2006 through September 2008. Cities, counties, villages and townships were the main culprits in failing to inspect bridges on time.

The audit also said 112, or 59 percent, of 190 underwater bridge inspections either were not done or were not done on time.

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By violating state law and federal regulations, the Michigan Department of Transportation could lose federal funding and approval for future projects, Auditor General Thomas McTavish said.

The Transportation Department agreed to comply with 10 recommendations from auditors, who were especially concerned inspections were not done for "scour" - erosion of stream beds or banks caused by flowing water near bridge piers and abutments.

Scour is the most common cause of bridge failure and collapse, according to the Federal Highway Administration.

In their response included in the audit, MDOT officials said they have been trying to complete the erosion evaluations and prepare response plans. The state said it repaired or replaced more than 450 river bridges in the past five years and has 24 more evaluations to finish by year's end.

Local governments have nearly 1,500 to complete by the end of the year, however.

Funding and staff reductions have left many local transportation agencies with little choice but to close bridges, MDOT spokesman Bill Shreck said Friday. But he stressed that most Michigan bridges were not mentioned in the audit because inspections had been done.

The bigger issue is a lack of money to repair not only bridges but roads, sewers and water mains, Shreck said.

"Without dependable revenue streams, governments at all levels will be less and less able to perform repairs and upgrade systems," he said.

Still, state officials said Michigan is in "substantial" compliance with federal rules, and they will strengthen guidelines so inspectors understand when bridges should be inspected more frequently.