A report issued by the University of Michigan’s Transportation Research Institute says a combination of lead-footed driving, improper auto maintenance and poor route selection can reduce a car’s fuel economy by as much as 45 percent. The report’s authors determined that the average real-world fuel economy in the U.S. is 17.4 mpg, far less than the 2011 new car model-year federal corporate average fuel economy mandate of 27.5. Tips to drivers to help cars operate more efficiently include ensuring the engine is properly tuned, oil changes at recommended intervals, and keeping tires properly inflated.