The objective of this study was to test the potential for NOx emissions improvements on a typical Euro 6 diesel vehicle, following modifications to its emissions control system, under Real Drive Emissions (RDE) testing conditions. A commercially available car was selected and was first measured in its original configuration according to RDE on the road and an initial conformity factor (CF) of 5.4 was determined. Subsequent engine calibration and installation of a Selective Catalytic Reduction (SCR) device were conducted and tested on a fully transient engine dyno setup, which precisely reproduced the engine operation under the on-road RDE test. The NOx reduction achieved with those upgrades was 90%, leading to a CF of 0.53, with no CO2 or fuel consumption penalty. These findings demonstrate that diesel vehicles can reach low NOx levels under real world driving conditions, when well-designed modern exhaust aftertreatment components are installed and properly calibrated.