It must be appreciated that some parts of the USA are a lot more ecologically minded than others, California being an outstanding example. Here, legislation is in place which actively encourages 'greener' cars and is acting as a major driver to shifting away from traditional fossil fuels.
There is also significantly more use of 'bio-diesel' in the USA than anywhere else in the world, much of it being produced from used vegetable oil originating from the catering industry.
To produce bio-diesel, the used oil is simply filtered, placed in a reactor with methanol (and an acid catalyst), left for a while and then out comes the fuel in the form of fatty acid methyl esters. This fuel, in addition to originating from renewable sources (rapeseed oil) also produces more power and less soot particles than conventional diesel.
I seem to recall the use of bio-diesel was being trialled on Swedish railways and has certainly been used to fuel buses in the UK although I don't recall the outcome of these.
hock: I get 45mpg average with my car, and I'm still struggling to be able to run it. Mind you, what do you expect when petrol is about £1.50 a gallon in America? 
