The Complex Environmental Story of Diesel

Diesel fueled vehicles are generally more fuel efficient than those fueled with gasoline. Biodiesel offers additional benefits (although flex fuel ethanol vehicles offer similar environmental benefits for vehicles primarily designed to run on gasoline). As a result of this fact, diesel vehicles now make up a large share of the European market, although they remain rare in the U.S. after the smoggy diesel vehicles of the 1970s left a bad taste in Americans mouths.

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