In general, bicycles can be taken on the metro outside rush hour. An extra ticket must be purchased for the bike.
Rush hour when bicycles are prohibited:
Mon. – Fri. 7:00 a.m. to 9:00 a.m. and 4:00 p.m. to 6:30 p.m.
A folding bike is considered hand luggage and can therefore be taken on the subway free of charge.