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EPA Estimates
Purpose
The intent of the EPA efficiency values posted on each new vehicle window-sticker is only to
provide a basis for comparison, not an actual MPG expectation... as commonly believed.
Read the fine-print on this scan of a 2004 Prius window-sticker:
Don’t be mislead by the big numbers. Real-World results vary significantly.
Ideal Conditions
Pay very close attention to the fact that the EPA tests are all performed under ideal conditions,
those that don't actually reflect real-world temperature or driving habits. Think of those values
reported as optimal, not realistic. You may be able to achieve them from occasionally, but not on
a routine basis.
Ranging Values
As mentioned on the window-sticker, there is a range of expected efficiency values. The large
numbers are really nothing but an average. In fact, the MPG isn't even constant for each vehicle.
Driving conditions, method of driving, and the influence of multiple drivers can all have a major
impact, causing fluctuation. Tank-to-tank measurements can vary quite a bit as a result, without
even taking into account the effect of seasonal cycles. None of these factors are represented when
the EPA tests are performed.
Unrealistic Speed
Back when the testing procedures were established way back in 1977, the speed limit on most
highways was only 55 MPH (88.5 km/h). That’s quite unrealistic for travel nowadays. Many
drivers cruise at speeds much faster. That causes a significant efficiency reduction, which is not
indicated on the window-sticker.
Unrealistic Climate
The "perfect summer day" climate portrayed during the testing is not what people actually drive
their vehicle in a great majority of the year. Winter extremes cause efficiency to drop significantly,
as do the Summer extremes. Factors such as temperature, wind, and moisture have a major
influence, causing the vehicle performance to be reduced in the form of lower MPG. To make
matters worse, the use of the Heater or A/C also contribute to lower MPG.
Prius User-Guide 12 of 45 Last Updated: 2/07/2006