They were commissioned by a European NGO, the international council on clean transportation (ICTT)[1]. The ICTT wanted to include diesel cars from the US market

They were commissioned by a European NGO, the international council on clean transportation (ICTT)[1]. The ICTT wanted to include diesel cars from the US market where regulation are stricter with intent to show that it was actually possible to have lower emission from diesel cars. As stated at the beginning of their report[2]: The Center for Alternative Fuels, Engines and Emissions (CAFEE) at West Virginia University (WVU) was contracted by the International Council on Clean Transportation (ICCT) to conduct in-use testing of three light-duty diesel vehicles, using a portable emissions measurement system (PEMS), over a variety of pre-defined test routes exhibiting diverse driving conditions pertinent to major United States population centers located in the state of California. You can also have a look at the ICTT report[3]. [1]: https://en.wikipedia.org/wiki/International_Council_on_Clean_Transportation https://en.wikipedia.org/wiki/International_Council_on_Clean... [2]: http://www.eenews.net/assets/2015/09/21/document_cw_02.pdf http://www.eenews.net/assets/2015/09/21/document_cw_02.pdf [3]: http://www.theicct.org/sites/default/files/publications/ICCT_PEMS-study_diesel-cars_20141013.pdf http://www.theicct.org/sites/default/files/publications/ICCT...