If I buy a 4 day travel pass AND I have activated it/used the first day, do I have to use the pass every time I travel during that period? (Would I have to use a travel day every time I travel on one of the trains during the activation period?) Or could I still buy a single use ticket for a particular day and save the remaining travel pass days for future use? This might happen if I want to take a quick regional train where a ticket would be inexpensive, so it might make sense to save the travel days for a longer more expensive trip. thanks