Taxes on vehicles and motor fuel play important roles both as sources of tax revenue and as policy instruments. First, fuel and vehicle taxes are often attractive fiscal instruments due to the comparatively low price elasticity of both car use and ownership. Second, the externalities of motorized traffic motivate pigouvian taxes on car use, such as carbon taxes and congestion charges. While taxes on car ownership and purchases are usually purely fiscal instruments, they are also increasingly motivated with climate policy arguments, for example subsidies for alternative-fuel cars.