Existing Tests and Methods:

Fuel economy estimates have been provided to consumers since the 1970s as a tool to help shoppers compare the fuel economy of different vehicles. Currently, EPA relies on data from two laboratory tests to determine the city and highway fuel economy estimates. The test methods for calculating these estimates were last revised in 1984, when the fuel economy derived from the two tests were adjusted downward – 10 percent for city and 22 percent for highway -- to more accurately reflect driving styles and conditions.

The city and highway tests are currently performed under mild climate conditions (75 degrees F) and include acceleration rates and driving speeds that EPA believes are generally lower than those used by drivers in the real world. Neither test is run while using accessories, such as air conditioning. The highway test has a top speed of 60 miles per hour, and an average speed of only 48 miles per hour.

Since the mid-1990s, EPA's emissions certification program has required the use of three additional tests which capture a much broader range of real-world driving conditions, including high-speed, fast-acceleration driving, the use of air conditioning, and colder temperature operation (20 degrees F). These conditions affect not only the amount of air pollutants a vehicle emits, but also a vehicle’s fuel economy. However, these tests were not required to measure fuel economy.

The New Methods to Determine Fuel Economy Estimates:

For the first time, the EPA fuel economy estimates will use vehicle-specific data from tests designed to replicate three real-world conditions, which can significantly affect fuel economy: high speed/rapid acceleration driving, use of air conditioning, and cold temperature operation. Previously, these conditions were accounted for by across-the-board adjustments, rather than by vehicle-specific testing.

EPA’s new fuel economy estimates will also reflect other conditions that influence fuel economy, like road grade, wind, tire pressure, load, and the effects of different fuel properties. The fuel economy for each vehicle model will continue to be presented to consumers on the label as city and highway MPG estimates.

In 2011, manufacturers will need to perform additional cold temperature, air conditioning, and/or high speed/rapid acceleration driving tests for those vehicles most sensitive to these conditions. However, in order to provide consumers with better fuel economy estimates sooner, EPA will use new calculation methods that capture these driving conditions. These estimates will begin with model year 2008 vehicles. The interim period from model year 2008 to model year 2011 will give manufacturers enough time to plan for this additional testing, while providing consumers with estimates that capture more realistic driving conditions.

How the New Test Methods Will Affect Fuel Economy Estimates:

Under EPA’s new methods, the new fuel economy estimates for most vehicles will be lower. This is not because auto makers have designed the same vehicles to be less fuel efficient – it is because our new test methods take into account factors that have been missing or not fully accounted for in the current tests. Because some vehicles are more sensitive to these factors than others, the impact of the changes will vary from vehicle to vehicle.

Compared to today’s estimates, the city mpg estimates for the manufacturers of most vehicles will drop by about 12 percent on average, and by as much as 30 percent for some vehicles. The highway mpg estimates will drop on average by about 8 percent, and by as much as 25 percent for some vehicles.
In vehicles that achieve generally better fuel economy, such as gasoline-electric hybrid vehicles, new city estimates will be about 20 to 30 percent lower than today’s labels, and new highway estimates will be 10 to 20 percent lower. The nature of current hybrid technology -- the addition of a battery as a second source of on-board power, sophisticated control systems, and sometimes a smaller engine – makes a hybrid’s fuel economy more sensitive to certain factors, such as colder weather and air conditioning use. However, many hybrid models will remain among the most fuel-efficient vehicles on the market.

Since driving behaviors and conditions vary, there is no test that can perfectly predict the fuel economy that every driver will get. With any estimate, there will always be times when a driver’s actual fuel economy will be higher or lower. However, EPA’s new test methods will do a better job of bringing the estimates on the window sticker closer to people’s real-world fuel economy experience.


Laboratory Tests Reflect Real-World Conditions:

It is essential that EPA’s fuel economy estimates continue to be derived from controlled, repeatable laboratory tests to enable a standardized or “level playing field,” comparison between all vehicle models. However, the underlying calculations to determine the estimates are based on data from real-world driving behavior and conditions. Laboratory testing also preserves EPA’s ability to confirm the results of manufacturers’ testing.

Auto makers will continue to be responsible for performing the fuel economy testing and calculating the label mpg estimates. EPA will continue to confirm the manufacturers' test results by performing audit testing at its National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan.