it is more to do with how the US EPA fuel economy tests and the posted fuel economy numbers are calculated, than to do with the Prius itself.
Most gasoline engines are most efficient at a higher, constant RPM. Since there is more steady and also more high speed driving done during the EPA's "Highway" test cycle, most traditional cars will have better fuel economy on the "Highway" cycle as opposed to the "City" cycle.
In the Toyota Prius, the gasoline engine is always kept at its most efficient RPM for the power demand. Under low power demands, the electric may solely power the car. Under more moderate demands, a combination of both electric and gasoline may be used. Even at higher speeds, the most efficient engine RPM may mean that the gasoline engine is more of a generator (recharging the hybrid battery) than directly powering the wheels.
So, when looking at the raw data (which is used for CAFE values), the Toyota Prius actually gets 64.8mpg on the "highway" test, and 66.6mpg on the "city" test. The raw data then has a downward multiplier applied (larger multiplier for the city test), to give a more "realistic" MPG which is what manufacturers have to advertise, taken from fueleconomy.gov . The Prius is about equally efficient at both the city and highway tests, but after the downward multipliers are applied, the Prius appears to have better city MPG than highway. EPA figures for the Toyota Prius is 48mpg city/45mpg highway.
http://www.epa.gov/otaq/cert/mpg/tes...e/07tstcar.csv
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
(In comparison, the Toyota Corolla Matrix automatic gets 42.3mpg on the "highway" test, and 30.5mpg on the "city" test. EPA numbers: 25mpg city/31mpg highway.)
http://www.fueleconomy.gov/feg/bymodel/Toyota2008.shtml
with the 2008 Toyota Prius why do you get better gas mileage in the town and city, then on the
Linear Mode
