Great way to save money on parking at IAD. Worked out very well for me on a two week trip. You show the reservation sheet at the front desk, pick up a rear view mirror tag, and park your car on the side or back. When you return, just get the car and go. Shuttle runs every half hour during much of day and every hour during late night. Upon return, call them to confirm the shuttle is coming. Double check these details with the hotel before booking.