The EPA’s change in estimating fuel economy is long overdue. Consumer Reports has been advocating for it for years. The old system, developed in the 1970s, does not accurately reflect today’s driving conditions, motoring habits, or vehicles. Many cars today spend 62 percent of their annual miles in stop-and-go traffic, where fuel economy is the lowest. Faster speeds are another big factor. The national highway speed limit was 55 mph in the mid-1970s, but vehicles now burn up to 15 percent more fuel per mile simply by traveling faster. Air conditioning, much more prevalent on new cars than it was 30 years ago, is also a factor. Running an air conditioner at 65 mph can reduce your fuel mileage by about 1 mpg and possibly more if you drive faster. The old EPA tests were conducted without the air conditioning turned on.

The new system is designed to address all of these changes. Additional tests will be run at higher speeds and while using the A/C, and will include a closer look at stop-and-go driving and more aggressive starts and stops. Cold-temperature tests are also being added to more realistically show what drivers in northern states can expect in winter.

Consumer Reports thinks the change will benefit consumers even if the lower numbers might be painful to look at in the showroom at first. A 2006 CR study showed that cars seldom meet the agency’s claims with the old system. We compared EPA figures with the mileage we measured in 303 cars and trucks for model years 2000 through 2006, and included mainstream, high-volume vehicles in a wide range of makes and models.

Our results showed that about 90 percent of the vehicles returned worse mileage than the EPA estimates. Gasoline cars averaged 9 percent fewer mpg. The biggest differences we found were in city driving. On average, the mileage was about 30 percent less than the EPA numbers. Our highway mpg more closely reflected the EPA ratings.

Consumer Reports tests fuel mileage in controlled conditions and in the real world. We use precise fuel meters spliced into the cars’ fuel lines, and adjust for outside temperature in our calculations. City mileage is conducted on our track using a 1.1-mile loop of stop-and-go driving combined with idling to simulate traffic and stoplights. Highway tests are done on a section of local interstate, run in both directions to minimize the effect of wind. We also drive all the cars on a 31-mile route that includes a mixture of highway, rural roads, and around-town driving. All tests are run several times using multiple drivers, and our overall mileage figure is an average of these tests.

While the new overall mileage ratings are closer to the results of our real-world testing, there are still discrepancies between the EPA’s lab-generated results and the mileage we got from driving the cars on roads. With the new system, our overall mileage is actually better than what the EPA predicts for some models.

Until the new system is in place, you can compare the old and new ratings online. The EPA is posting both mileage estimates for models going back to 1985 as well as an explanation of how their methods have changed, at www.fueleconomy.gov. Click on “New fuel economy ratings” on the home page. Fuel mileage for all models that Consumer Reports has tested can also be found in our individual vehicle profiles.

The theory behind hybrid cars

What sets hybrids apart from regular cars is that they essentially use two powertrains, an electric motor and a gasoline engine. The electric motor draws its power from a large battery pack that is recharged by the gas engine and by energy recouped from the brakes.

The electrically powered car has been a vision for the future for decades, but its development reached a virtual dead-end in the mid-1990s. That’s when hybrids emerged, promising a compromise between the benefits and limitations of both electric and gasoline powertrains.

Electric motors are very efficient at accelerating, and unlike their internal-combustion counterparts, produce their maximum power from a dead stop. But batteries with enough energy to drive long distances cost too much, are too heavy, and take up too much space in a car. Theoretically, a hybrid solution is the best of both worlds. By relying on electric power, at least some of the time, there is a clear benefit in reducing emissions.

By using electric motors for acceleration, automakers could use smaller, more-efficient gasoline engines to supplement the motors under heavy load (i.e., acceleration, hills) and to cover long distances. By combining the two systems, the battery packs can be relatively small. The downside of a hybrid is that the dual drivetrains can be significantly more expensive than a traditional gas engine alone, the battery pack takes up space, and the pack adds weight.

Full and mild hybrid cars

Hybrids today fall into one of two categories: full and mild. The main difference is whether or not the car can propel itself solely on electric power.

Full hybrids like the Chevrolet Tahoe, Ford Escape, Nissan Altima, and the Toyota Prius and Camry can start off silently, creep in stop-and-go traffic and putt around town at low speeds on just electricity. The gasoline engine kicks in as soon as the driver demands quicker acceleration to supplement the electric power. The engine can also turn off when the car is slowing down or coasting. Full hybrids are more expensive to produce, but they typically save more fuel and run cleaner, especially in city driving.

Mild hybrids like the Chevrolet Malibu and the Saturn Vue Green Line can shut the engine off when the car is stopped and restart it as soon as you take your foot off the brake pedal. They use electric power only to assist the gas engine on hills and when accelerating. Mild hybrids produce only a modest gain in fuel economy yet command a purchase-price premium.

Both types save gas by shutting down the gas engine at stops. The Prius uses a smaller gas engine than the similar-sized Toyota Corolla. Other vehicles typically use the smaller of the available gas engines in the equivalent nonhybrid models. All of them also use the electric motor to recoup some of the energy it takes to stop and use it to charge the batteries.

Driving these hybrids is really no different than driving other cars, except that the engine sometimes stops and starts by itself. At first it might seem a little strange but it’s easy to get used to, especially if the transition to gasoline-engine operation is smooth. In fact, some hybrids feel smoother than comparable four-cylinder economy models because the electric motor is quiet and the gas engine is less strained under low-speed acceleration.

None of the hybrids on the market today need to be plugged in, and none can be. The batteries are recharged only by the gas engine and by braking. Just fill the tank with gas and go.

The best hybrids offer significant gas savings. The Toyota Prius, for example, returns the highest gas mileage of any five-passenger car we have ever tested – 44 mpg overall. The midsized Toyota Camry hybrid returns 34 mpg, better than many small cars. And the Honda Civic Hybrid returns an excellent 37 mpg. The only nonhybrid car that gets close to such excellent fuel economy is the 2009 Toyota Corolla, at 32 mpg overall.

Other hybrids, however, offer moderate gas savings in larger vehicles while improving acceleration and maintaining utility. The Toyota Highlander Hybrid and Lexus RX400h, for example, get 24 and 23 mpg, respectively. Not stellar, but about 25 percent better than their gas siblings. Both use relatively large 3.3-liter V6 engines.

In terms of emissions, hybrids typically produce 29 percent less smog-forming nitrogen oxide than conventional cars, according to a study by the American Council for an Energy-Efficient Economy. And every gallon of gas saved reduces carbon dioxide emissions by 19 pounds, which reduces global warming.