It takes longer than continuous biking in a city would make one think, for the same reason driving does: you have to stop at red lights, yield, wait in traffic.
Living in a small city (or large town may be a more accurate way to put it) with lots of greenways, I feel like I get the best of both worlds. Before my office re-located I could go 6 miles (~9.5 km) to/from work on a bike in between or around corporate campuses and subdivisions and only deal with a few intersections, while in a car I'd have to deal with traffic and traffic lights regularly most of the way.
