The contracting organization, a European non-profit, had wanted to convince European regulators to emulate strict U.S. standards for diesel emissions of nitrous oxides (NOX). So it asked CAFEE engineers to gather data from the field. They rented VW diesels, measured their tailpipe emissions on the road and compared them to measurements on the same cars made in the lab. The discrepancies were huge.
http://spectrum.ieee.org/cars-that-think/transportation/adva...