2. City Subway
Subway is one of the means of transportation in major US cities. You can take the subway in cities like New York, Los Angeles, Boston, San Francisco, Chicago, Atlanta, and Washington D.C.
To use the subway, you must have a Tap Card or a Metro Card. There are card machines at subway stations; you buy, make a card, then top up the full amount for the amount of time you want to go. Usually, you can buy a 1-day, 7-day or 1-month pass. The advantage is that you can ride the subway unlimited times with the purchased card.