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Neptune
"ultra low" emissions compared to what? I doubt that these can be as low as a less heavy vehicle that would consume less.
The best explanation I could find was here: ULEV (Ultra Low Emission Vehicle)
http://en.wikipedia.org/wiki/Ultra_Low_Emission_Vehicle
They are pretty much based on the same stringent guidelines, as they all have to meet or exceed a certain goal/criteria to be classed as such.