The european tests (NEDC) are more forgiving than the new EPA test, and roughly comparable to the old EPA test. If we want equal comparisons, we should use the epa for new cars, the revised epa for old cars like mine, and a ~15% lowered adjustment for the euro ratings to roughly match the new epa.
2010 Prius (I converted the L/100km numbers into US mpg):
EPA: 51 city / 48 hwy / 50 combined
NEDC: 59 city / 62 hwy / 59 combined
EPA is 85% of NEDC.
2007 Prius (that has both old and new ratings):
Old EPA: 60 city / 51 hwy / 55 comb
New EPA: 48 city / 45 hwy / 46 comb
New EPA is 84% of old EPA.
VCAcarfueldata.org.uk - Search Results - Further Information
Model 1 Vehicle Characteristics
http://www.fueleconomy.gov/feg/compx...Field=Findacar