The U.S. Postal Service could reduce its maintenance costs by $21.8 million a year by improving oversight of its mechanics and right-sizing staffing at vehicle garages, according to finding by the U.S. Office of Inspector General.

By implementing recommendations from the report, the USPS would save 431,129 work hours, which adds up to $21.8 million.

Vehicle maintenance facilities weren't operating at peak efficiency when compared to established targets, the report found. Work order hours that exceeded timecard hours, which is known as undistributed labor, accounted for 11% of total maintenance labor costs and exceeded the established target of 3%, according to the report.

The report cited a lack of supervisory oversight as a driver of the higher costs. Overhead, including supervisory and support labor costs, accounted for 24% of total maintenance costs, which were lower than the established target of 24%. The maintenance facilities had 109 vacant administrative and supervisory positions.

The USPS maintains its fleet using 316 vehicle maintenance facilities that service 211,264 vehicles. The USPS also contracts with commercial garages for maintenance and repair. In fiscal year 2014, the USPS spent $1.1 billion on maintenance expenses.

The inspector general's office audited facilities in the Capital Metro and Pacific areas during fiscal year 2013 to assess maintenance operations in the Eastern, Great Lakes, Northeast, Southern, and Western areas.

Read the full audit report here.