I think it gets even more interesting when you travel that way only: for one thing, you can get a public transit path (usually around $50 a month, but here in France it’s half-price for university students, and if you’re working your job pays half of it too. Reduces it to about €10 a moth if you’re a student with a job).
And on top of that, if you only use public transit, you don’t own a car. Which means you don’t have the car expenses that you would if you owned a car and took the bus (car insurance, the price of the car itself and so on)
Also, depending on where you live, finding a place to park makes using your car longer than using public transit. That’s certainly the case here in Paris, although it’s probably less of an issue in North America.