That's the point of carbon taxes, isn't it? It's irrelevant what and how people drive, and they certainly don't give a buck about carbon emissions, yet they unwittingly alter their behavior with the effect of reducing the taxed behavior.

By the way, diesel is now typically more expensive than gasoline in Europe too, and the tax embodied in the price is roughly proportional to the carbon content of both. In the past there used to be a lower tax on diesel in some countries as an aid to farmers and the transport industry, but it is less common now.