Top 10 Passenger Cars for Fuel Economy

No organization tests every vehicle's fuel economy in real-world driving. The challenge of obtaining every vehicle early in the model year, then driving them all over a specific route under identical conditions, is insurmountable. Therefore, we have to rely on Environmental Protection Agency estimates. While you can't expect your vehicle to get the exact mpg figures supplied by the EPA, mileage estimates do let you compare vehicles.

EPA Estimates: A Flawed but Helpful Yardstick in Comparing Vehicles

Because the EPA's primary concern is emissions, its fuel-economy estimates are secondary. All are based on simulated driving. Professional drivers operate tested vehicles in identical patterns under controlled laboratory conditions, with the tires rolling on a dynamometer. The EPA explains that the test simulates road and aerodynamic forces, but the vehicles are never driven on an actual road.

Two tests are conducted — one for city driving and a second for highway operation. The city test simulates an 11-mile urban stop-and-go loop, with an average speed of 20 mph and a short stretch of simulated freeway driving. The trip lasts 31 minutes and has 23 stops, and 18 percent of the time is spent idling. The highway simulation is a 10-mile trip at an average speed of 48 mph, with no stops and little idling.

Fuel-economy estimates are actually calculated from the emissions generated during these tests. Adjustments are made before coming up with final figures, based on studies showing that real drivers achieve 90 percent of the EPA's city estimate and 78 percent of its highway estimate.

In real-world driving, a vehicle's actual fuel economy may not be as high as the EPA's estimates, and this applies to hybrid-powered vehicles like the Toyota Prius, too.

Critics charge that in real-world driving, vehicles get far fewer miles per gallon than the simulations suggest. That may be because the test has not changed in the past three decades. Most people use air conditioning today, but that's not accounted for in the simulation. Also, traffic congestion is much greater now than it was in the 1970s.

Owners of hybrid-powered vehicles may also observe lower real-world fuel economy than the EPA's estimates. Automotive News reports that the EPA is determining if it should modify its test conditions for hybrids in order to better align its estimates with observed fuel economy.

How You Drive Affects Fuel Usage

Some people complain that they can't obtain EPA estimates with their vehicles. However, in addition to possible test flaws, a close look at their driving habits may explain why. If you stomp on the gas pedal when starting off from a stoplight, drive at excessive speeds on the highway or run with underinflated tires, your mileage is sure to be considerably lower than the estimate suggests. Running the air conditioner also consumes quite a bit of extra fuel.

If your travels take you through cold weather, understand that your fuel mileage might be negatively affected.

Extra weight, like a full load of passengers or cargo, makes engines guzzle more gasoline than if only one or two occupants were inside. Hilly terrain and cold-weather driving also cut into gas mileage.

Detailed information on EPA testing can be found at www.epa.gov and www.fueleconomy.gov. The EPA's Green Vehicle Guide gives air pollution and greenhouse gas scores for many vehicles.