BS VI or Euro VI Norms mandates the RDE emission compliance for the diesel commercial vehicles. Development of the engine- after treatment system for meeting these requirements needs a greater insight into the emission behavior of the vehicle under current norms i.e. BS IV and Euro V. In other words, quantifying the on road emission of current vehicle will be helpful in developing engine/vehicle for RDE emission compliance. In the current study, the focus is on the assessment of real road NOx emission of a BS IV and Euro V complaint diesel commercial vehicle.The real road emissions of vehicle have been quantified using the onboard NOx sensor mounted on the after treatment system outlet along with a validated exhaust gas model developed and parameterized in engine control unit. The real road NOx emissions were compared with the test bench emissions for various conditions. The NOx emission coefficient defined as the ratio of real road NOx emission to the test bench emission was used to assess the behavior of the given vehicle. Furthermore, the influences of the vehicle load, driving pattern and ambient conditions of pressure and temperature on NOx emission coefficients have been discussed.