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5 Things You Need to Know About EPA Fuel Economy Estimates
By Wendy Clem
What Does it Mean?
The Environmental Protection Agency (EPA) studies cars through a series of tests dedicated to estimate a vehicle's fuel efficiency. The goal is to simulate actual driving conditions and identify the likely miles-per-gallon a car is capable of achieving during city and highway driving under normal everyday conditions. These figures are included on all new vehicle "window stickers" – or Monronies – to allow a basis of comparison between new car models.
New Methods Were Needed
For many years, consumers complained that the estimated fuel economy identified by the EPA was far too optimistic and that new testing methods should be used. After years of controversy, the EPA instituted all-new testing protocols with the 2008 model year, with this testing better reflecting realistic driving situations that can lower fuel economy l such as aggressive driving, higher speeds, use of vehicle accessories like air conditioning, and starts in cold weather.
What Were the Old Standards?
Tests done in 2007 and earlier years involved the dynamometer, a stationary device that has been used to simulate actual street driving since 1985. On a dyno, a car is "driven" in place with its wheels spinning large rollers under specific conditions. In the past the conditions simulated a 75 degree day and the use of no accessories. These conditions contributed to unrealistically optimistic fuel efficiency estimates since accessories like air conditioning are often used in real life, and these accessories are often powered by the engine. An air conditioning compressor's drag on an engine diminishes overall efficiency and negatively impacts fuel economy. Also, driving under different temperatures also can influence efficiency. The dyno tests followed a certain protocol. During a "city" trip beginning with a cold motor and covering 11 miles over 31 minutes, 23 "stops," and 18 percent time idling, there was a maximum speed of 56 miles per hour and an average speed of 20 miles per hour. For the "highway" trip beginning with a warm engine, lasting 10 miles and 12.5 minutes with no "stops" or idling made, the maximum speed was 60 miles per hour and averaged 48 miles per hour.
EPA's Revised Tests
The EPA revised its test methods with 2008 and later models to more accurately reflect real-world mileage. The dynamometer is still used to analyze fuel efficiency under laboratory conditions, but important changes in the process include higher speeds of up to 80 miles per hour to reflect the kind of driving actually being done on the highway. Also, colder temperatures beginning at 25 degrees instead of 75, faster acceleration, and the use of accessories is applied. These estimates have been appearing on the window stickers of models manufactured after September 1, 2007. To provide a basis for comparison with the old testing regimen's mpg estimates, automakers are also be able to affix another label through June 2008 indicating what the estimates would have been using the previous test methods.
What Are the Projected Results?
With the new testing procedure, city fuel economy estimates decreased, in many cases by 10-20 percent, with a . drop of about 5-15 percent in highway estimates. Fuel economy projections for hybrids suffered disproportionately with many estimates moving considerably downward. At present, only vehicles with a gross vehicle weight rating up to 8,500 pounds are included in the regulations. Vehicles rated between 8,500-11,000 pounds will also be regulated as of 2011.
Wendy Clem is a Michigan-based writer/photographer providing material for newspapers, magazines, and online - - locally, regionally, and nationally. Her syndicated auto column for Avanti NewsFeatures has appeared in 400 national markets, and her online how-to articles serve an international audience. Wendy holds a Bachelor of Fine Arts degree in journalism from Detroit's Wayne State University.
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