From http://www.takepart.com/open-letter-to-california-air-resources-board-ch... The VW emissions scandal is mainly the result of physics meeting fiction. In the simplest terms, we have reached the point of de miminis returns in extracting performance from a gallon of diesel while reducing pollutants, at least at reasonable cost. Unsurprisingly, and despite having the greatest research and development program in diesel engines, VW had to cheat to meet current European and U.S. standards. Meeting future tighter diesel standards will prove even more fruitless.
For a significant fraction of the non-compliant diesel cars already in the hands of drivers, there is no real solution. Drivers won’t come in for a fix that compromises performance. ///