Roof racks stay on the car. You don't take it off once it's on there, unlike a trunk rack.

Hitch racks typically stay on, too, although I understand they are fairly easy to remove.

Right now I can fit my regular bike inside my VW Rabbit with the front wheel off and the back seats down. I can fit my Bike Friday in the way back of my Rabbit without messing with the seats.

In fact, it would be a whole lot cheaper to get a really nice folding bike instead of a new car...something you might want to think about.