 CHAR: When John and Zeus are in Tompkins Square Park they see that  they are being sent to Yankee Stadium, and thus John says, "Where is  the nearest A train?" The three subway lines that go to Yankee  Stadium are the B, D, and 4. At Tompkins Square Park the closest  subway line to them happens to be the 4 train, regardless of their  destination, thus it would not even make sense for them to walk  across town to the A train and transfer lines at a later point.