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EPA Fuel Economy Estimates for Model Years 2008 and Later

Changes to Consumer Fuel Economy Estimates

In response to complaints that the fuel economy values on new vehicle labels were too high, the U.S. Environmental Protection Agency (EPA) adopted new methods to estimate fuel economy for cars and light trucks, starting with the 2008 model year. These new estimates, which were intended to better reflect “real world” driving conditions, were part of a regulation that brought into effect three important changes:

- More accurate mile per gallon (MPG) estimates. EPA now includes previously omitted factors such as high speeds, quicker acceleration, air conditioning use and cold temperature driving in its estimation of fuel economy;

- Beginning with 2011 model cars, fuel economy labels for heavier SUVs (up to 10,000 pounds); and
- Changes in the overall design of the fuel economy labels displayed on new vehicles. The label now shows a “combined” fuel economy, in addition to city and highway values, enabling consumers to compare overall fuel economy between vehicles more easily.  

These changes serve to improve consumer information but have no direct impact on average fuel economy. Manufacturers’ Corporate Average Fuel Economy (CAFE) levels depend on “unadjusted” test results, which are much higher than new label values.

How were Fuel Economy Estimates Affected?

Fuel economy estimates are generally lower under the current method than previously. This is because the estimation methods take into account factors that were omitted in the pre-2008 fuel economy estimates (see below). However, the impact of these changes varies among vehicles, as vehicles are differently sensitive to each of the factors mentioned below. At the time of the change, EPA anticipated the following effects on fuel economy estimates:

- City MPG estimates would fall by 12% on average, with some vehicles seeing as much as a 30% drop in fuel economy

- Highway MPG estimates would fall by 8% on average and by as much as 25% for some vehicles

- For higher fuel economy vehicles such as hybrid vehicles, city MPG estimates would fall by 20-30%, while highway MPG estimates generally would be 10-25% lower. These vehicles tend to operate at high efficiency under ordinary driving conditions, and adding air conditioning and aggressive driving loads may reduce their fuel economies more than those of less efficient vehicles.

- Combined MPG estimates would fall by an average of 6%. Under the new 5-cycle methodology, combined fuel economy is calculated using a weighting of 43% / 57% city/highway, respectively, based on actual driving patterns, while the weighting was previously 55% / 45% city/highway. It should be noted, however, that the combined MPG shown on the label and on government web sites retains the 55% / 45% weighting and therefore likely understates average fuel economy for most vehicles, given that the city value is typically substantially lower than the highway value.

New Methodology – 5 Cycle Testing

In order to determine average city and highway fuel economy estimates, EPA previously used tests carried out under standard conditions of 75 degrees Fahrenheit and only included maximum acceleration rates and driving speeds significantly lower than those attained by actual drivers.

The new methodology uses a 5-cycle testing procedure that supplements the basic city and highway fuel economy tests with tests designed to address fuel consumption associated with aggressive driving, air-conditioner use and cold temperature driving. Below is a brief table that outlines the test conditions of the individual tests that are used to determine average fuel economy.

Test

Driving

Ambient Temperature

Engine Condition at Start

Accessories

FTP

Low speed

75°F

Cold and hot

None

HFET

Mid-speed

75°F

Hot

None

US06

Aggressive; low and high speed

75°F

Hot

None

SC03

Low speed

95°F

Hot

A/C on

Cold FTP

Low speed

20°F

Cold and hot

None

Fig. 1 Key Features of the Five Current Emission and Fuel Economy Tests

For consumers, the change in EPA’s methodology means that fuel economy estimates from 2008 onwards cannot be compared directly to label fuel estimates from previous years.

 

How to buy green

Sorting out Standards

EPA Fuel Economy Estimation (Cars and Light Trucks)

Why Buy Green?

Automobiles and the Environment

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