That 55-mile-per-gallon hybrid car you've been eyeing may end up being a 44-mpg hybrid. The federal Environmental Protection Agency announced a new system Monday for evaluating fuel economy that will lower mileage estimates for most vehicles. On average, vehicles rated under the 2008 method will post a 12% drop in city gasoline mileage and an 8% decline in highway mileage. With the new testing requirements, the EPA is attempting to come up with estimates that more closely reflect the real-world mileage motorists can expect when they purchase a vehicle. Under the current system ... actual mileage is often far lower than the posted EPA ratings. Hybrids will be hit harder because the new test eliminates some of the all-electric driving that helped them produce impressive results. A recent study ... found that the average mileage for passenger cars and light trucks was about 14% less than EPA estimates. The mileage for gas-electric hybrids probably will be 20% to 30% lower than present estimates for city driving and 10% to 20% lower on the highway. These vehicles quickly lose their all-electric advantage when operated in cold weather or quickly accelerated. The new EPA mileage estimates won't harm automakers' ability to meet federal rules requiring an industrywide average fuel economy of 27.5 miles per gallon for cars and 21 mpg for sport utility vehicles, pickup trucks and vans.