the period of transition from nedc to wltp has started in 2017 and will end in september 2019. car manufacturers were required to obtain approval under both wltp and nedc for any new vehicle from 1st of september 2017, while wltp superseded nedc from september 2018. from that date, measures of fuel consumption and co emissions obtained under wltp are the only one with legal validity and are to be inserted in official documentations (the certificate of conformity).