| http://yosemite.epa.gov/opa/admpress.nsf/68b5f2d54f3eefd28525701500517fbf/be19cb23762789a685257241006a9857!OpenDocument and http://www.greencarcongress.com/2006/12/epa_issues_new_.html Prior to the 2008 procedures:
"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% for city and 22% 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." Post-2008 procedures:
" 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."
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