I rode the entire GAP-C&O trails last June with a couple of friends. Here is what we did. We drove to DC with our bikes, and left the car at a relative's house in Bethesda, MD. We then packed up our bikes and rode to Union Station in DC, arriving about 2 hours before departure. That gave us plenty of time to pack our bikes in the Amtrak boxes and get something to eat. We took the train to Pittsburgh, arriving close to midnight, unpacked our bikes and rode to our hotel in the dark. We all had good LED lights, which are useful for the tunnels as well. We headed back toward DC the following day, averaging about 60 miles a day. We reached Georgetown in 6 days and rode from there to the home where we left our car. If you don't know anybody in DC, you could park your car at the Reagan airport. Parking is very expensive in DC, as you probably know.