Yonah Freemark (see his April 12 post) cites a great case where Pennsylvania tried to fund rail using a toll tax on the highway. That turns out to be not legal.
But this is even more fascinating. California and other states are raising taxes on highway use, such as license fees. But raising prices actually depresses demand. With driving on the decline, higher taxes for cars, licenses and fines will only accelerate the decline in driving, yielding even less income for states.
So taxing drivers more won't help to fund highways, much less trains. How do you think we should fund either roads or rail? Tell us your ideas.