Then you'd have to level the playing field. Make drivers pay for the full cost of the roads by raising the gasoline tax, a lot. As it is, taxes from all sources find their way into building and maintaining roads. If the full price of roadways were shifted solely to those who use them, you'd be surprised at just how much public transportation makes sense.
The problem is that everyone bitches about 'their' money being spend on public transportation, without a thought to all the money spend on roadways that comes from a variety of sources that have nothing to do with use. It's a cognitive disconnection that most people don't even realize they have.