Less is more
I know regular non-hybrid car could get 50-70 mpg fairly easily. But there is no demand for low power cars.
My dad's Aveo is one of the slowest cars built in 2005. And it's plenty fast enough (103hp). But I guess the normal american would say It takes over 10 seconds to get to 60 that this is brutally slow (10.8 seconds if you were wondering).
Anyways what i am saying is you can't get crazy good mpg with lots of horsepower. A Honda insight with a geo metro engine in it would get almost the same milage as stock (maybee higher because it wouldn't have to carry the batteries around).
http://www.micro-car.co.uk/themc1car.htm
^ this car can do 72mph with only 21 hp. Thats a bit slow but with a few more HP (maybee an added turbo) it could keep up on the highway.
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2008 EPA adjusted:

Distance traveled by bicycle in 2007= 1,830ish miles
Average commute speed=25mph (yes, that's in a car)
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