the tax rates are higher for diesel vehicles in order to address their higher impacts on local air pollution diesel cars with particle emissions equal or above gkm are also subject to an extra tax eur while the vehicle taxation reform is a step forward taxes on purchase and ownership of vehicles are less efficient than fuel taxes and road charges in reducing emissions since they are more distant from actual vehicle use moreover in the portuguese case they provide very and possibly disproportionately strong incentives to abate c emissions compared to the incentives faced in other sectors of the economy eg in those participating in the eu ets the tax rates rapidly increase with the level of c emissionskm and are much higher in portugal than in other oecd countries oecd b the average c emission rate of new cars average c emissions per km sold in portugal has greatly declined at gkm in compared to the eu average of gkm