Transport services like airports, airlines, and ferry services, and in some cases trains and buses, may provide 24-hour service. Examples of public transport services operating 24/7 include the New York City Subway, PATCO, the Copenhagen Metro, and two lines of the Chicago "L". Some public transportation services, including two lines of the SEPTA system, some lines of the London Underground, the Barcelona Metro, and the Istanbul Metro, only offer 24-hour service on Friday and Saturday nights.