Epa Fuel Economy Testing

After the Prius was released, there was a lot of outcry about why the advertised fuel economy was higher than that which people experienced.  And what about that little asterisk that says “EPA Estimated City MPG” after billboards tout 60 MPG?  And why are the numbers published for the 2008 models lower than those for the 2007 models?  Well, it all boils down to those EPA fuel economy tests.

The Old Methods for Testing

EPA laboratory fuel economy testing began in the 1970s as an effort to help consumers compare vehicles based on fuel economy.  Estimates were determined for both city and highway driving.  In 1984, the city test was adjusted downward by 10% and the highway test was adjusted downward by 22% in an attempt to more accurately reflect real world scenarios.  Since then, testing methods have not changed.

Both tests have been performed in mild climate conditions of 75 degrees F.  Acceleration rates and driving speeds employed in the tests are believed to be generally lower than those of drivers in real world conditions.  For example, the highway test had a top speed of 60 miles per hour and an average speed of 48 miles an hour.  Real world drivers go much faster than this.  Additionally, in old EPA tests, no accessories (such as air conditioning) were running during testing.

The New Methods for Testing

In 2006, the EPA finalized new test methods that went into effect for 2008 models.  According to the EPA’s fuel economy fact sheet, “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…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.”  

In 2011, manufacturers will be required to perform additional testing for cold weather, for air conditioning, and for high speed driving with their vehicles that are most sensitive to those driving conditions.  However, until then, the EPA is employing new calculation methods in order to publish more accurate statistics for consumers.

Look for stickers like this one:

What does this mean for you?

With the new testing methods in place, you can expect to see lower estimates for fuel economy for most vehicles.  Now, don’t think that the vehicle is less efficient than older models.  It’s just that the new methods take more realistic factors into account that until now have been missing.  According to the EPA:

“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.”

The Bottom Line

The EPA maintains that these tests must continue to be performed in controlled settings inside a laboratory and must be repeatable.  Therefore, consumers must remember that fuel economy estimates are just that – they’re estimates.  At the very top of the EPA’s fuel economy homepage, there is a disclaimer that says, “IMPORTANT REMINDER: EPA's fuel economy estimates are designed to allow consumers to comparison shop. Your fuel economy will almost certainly vary from EPA's fuel economy rating.  This is based on a number of factors, such as weather, road conditions, your driving and maintenance habits, and your use of air conditioning.”