But, a study in the Netherlands where diesel vehicels are common show that there are limits to these benefits.
A small percentage of "superpolluters" (here 5%) account for a high percentage (here 43%) of the pollution.
Most of those superpolluters turn out to be diesel fueled vehicles. Thus, while diesel vehicles are an environmental plus when they in good shape, diesel vehicles that need a tune up (or worse) can be a dominant cause of car based air pollution.
If we do make a major transition to diesel vehicels, therefore, it should be accompanied by more stringent emissions tests than those applied to gasoline based cars. Unfortunately, my understanding is that that Colorado is considering the opposite policy decision, loosening emissions testing for diesel powered motor vehicles