>They'll probably increase as gas motor cars are phased out before the process ever sink too low.
Why?
Why?
I don't see diesel going away so soon though because of industrial, agriculture, and military use. It will probably be taxed differently according to it's use. In fact it already is taxed differently in the US for home heating, vehicle, and aviation use.
If it's about revenue, taxing combustion engines gets less attractive the smaller the market becomes especially if it's easy to switch.