Manufacturers optimize cars for 46-58 mph, since most of the EPA Highway test and 6% of the City test are at these speeds. The 1990s pattern graphed below has probably not changed much, since the EPA test has not changed. The best efficiency was usually between 46 and 53 mph. One car's best speed was below this range, and one was above. (Spreadsheet & other data at CO2List.org Full study at Fuel.NumbersInstitute.com )

Last Updated on 3/5/2009
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