Emissions certification is based on emission and fuel consumption tests on roller dynamometers. Mercedes-Benz Cars uses considerably more than three dozen roller dynamometers on three continents in Germany, USA and China for certification and development. The introduction of the WLTP legislation with the new WLTC test cycle means that the time-to-certification has increased significantly, also because of the special requirements for plug-in hybrids and electric vehicles.

D548722 Mercedes-Benz Cars - Technology and Emission Strategy