If you're one of the "Normal"(whats normal these days anyway), average American, living car-free will most likely depend on where you live, and how far your workplace is.

If you live in some suburbs, 40 miles from the regional center(usually a downtown of the biggest city nearby), with buses coming in at 1-2 per hour, or no bus service at all, then you absolutely need a car. No, the lifestyle demands it. Renting a car might be feasible but that gets uneconomical, and using your bike depends on wether or not you want to commute in a bike-hostile environment, or you can bike one way, and park in a designated parking station in one of the bigger public transit stations, and use trains/buses on the second half. But I don't think you can never truly be car-free, unless you're one of the hardcore car-free types.

If however, you live in a bigger city, a bit denser city or area, then it is more convenient, and frankly, easier. You can integrate your bicycle, public transit, walking and renting a car much, much easier. Again, there are exceptions, but usually, the closer you are to a dense area, the better off you'll be in car-free terms.