I used to run a LOT, ran track and cross-country all through high school and into college. But one time I was running a fairly long road route trying to whip myself into shape for a triathalon and right about the point where I was going to turn around and head home my left knee started hurting pretty bad and man that was a long gimpy walk home. Ever since then I really haven't run a lot, but if I were to get back into it I'd do it so I'm always within a pretty short walking distance to the car whether that means on a treadmill in the gym or maybe the track at the high school.