They do measure emissions in
grams/mile, but if a vehicle was large enough it used to be able to get into a relatively favorable emissions bracket, eg a 2003 H3 may have gotten by w/ more pollution in g/mile than a 2003 TDI powered VW. As of 2009 everything up to 10000 GVWR has to conform to the same standards if I'm reading that correctly, so everything is pretty fair. If a small diesel compact can't get below .07g/mile of NOx while a full size diesel Dodge pickup can, then I agree w/ the standards dictating that it shouldn't be sold here.