The vehicle stock module calculates the size and composition of the car stock. Its output is a full description of the car stock in every year, by vehicle type, age and (emission) technology of the vehicle. The vehicle stock is represented in the detail needed to compute transport emissions. The integration of the car stock module in PLANET will allow to better capture the impact of changes in fixed and variable taxes levied on cars. Among these impacts, the effect on the environment is of particular interest.