WASHINGTON, D.C. --- The federal Environmental Protection Agency this week unveiled a new system for measuring fuel economy. The new testing requirements are expected to lower mileage estimates for most vehicle models, but provide a more accurate picture of what mileage a vehicle will get in the real world. According to a recent study by Edmunds.com, the average mileage for passenger cars and light trucks is about 14 percent less than EPA estimates. The new measuring system will affect hybrids even more than other models because it eliminates some of the all-electric driving. According to a report in the Los Angeles Times, a hybrid car whose mileage is now estimated at 55 miles per gallon may be marked down to 44 miles per gallon when the 2008 models arrive under the new system. Bill Wehrum, the EPA's acting assistant administrator for air and radiation, told the L.A. Times that on average vehicles rated with the 2008 system will post a 12 percent drop in city gasoline mileage and an 8 percent drop in highway mileage. Mileage for gas-electric hybrids will likely be 20 to 30 percent lower than present estimates for city driving and 10 to 20 percent lower on the highway. The EPA will also begin estimating mileage for medium-duty pickup trucks, vans and SUVs that weigh between 8,500 and 10,000 pounds. These vehicles were previously exempted from the EPA ratings. However, vehicle manufacturers won't be required to publicize big trucks' mileage estimates until the 2011 model year. What has led to the discrepancy between EPA estimates and real-world mileage under the existing system? Simply put, the testing was conducted under ideal conditions. Agency testers didn't include much stop-and-go driving in traffic, rapid acceleration, driving with the air conditioning on, or driving in cold temperatures. The new system will take those real-world conditions into account.