I'm not sure people are going to want to pay a tax explicitly for roads on their air conditioning bill. A tax at the pumps works to show a tax is being collected by the users of roads and to show road users are paying their way, an electricity tax wouldn't. Right now a Hummer driver pays a huge amount of tax, whereas an electric Hummer driver would pay much less because a 35% tax on electricity is never going to happen.
Okay, I was just speculating. But realistically, I can't see any kind of road tax that involves tracking users. That might fly in Europe. Can't see that here. We tend to be much more prickly about privacy than they are. More than likely we'd just have some kind of flat tax tied with the registration of the car.
Anyway, my point was that you don't need to penalize the car to make rail attractive. It already is. We've just structured passenger rail pricing badly. And the services aren't competitive with the car. Heck, keep the same price and speed it up so it's marginally competitive with the car (it takes longer door-to-door today with the train) and you'd get more customers.