I live in Fairfax. When I ride down w/ my dad (who lives in Ashburn and takes me w/ him sometimes), it takes us about 40-60 minutes (given traffic). We go to lot 8 to park. Metro will take a full hour to get there, so you'll have to allow 15 min. to get from car to train and 15 from train to RFK. Where in fairfax are you?