Personal anecdote. I am a student. In the town where I live, university students (and faculty and staff if I'm not mistaken) can ride the municipal buses for free. This has had an enormous impact on my behavior, even versus a very small charge like 25 cents. I don't often carry cash, and maintaining a fare card is a hassle, so if I had to pay for the bus I probably wouldn't use it very often. But since I can hop on to any bus I happen upon without worrying about paying or figuring out which transfers I need, I use it all the time.
