With six tracks (4 Green Line, 2 Red Line), Park Street is undeniably the hub of Boston's subway system. Track 1 is used by outbound trains to Cleveland Circle or Riverside, Track 2 by outbound trains to Boston College or Heath Street, Track 3 by inbound trains terminating at Park Street, and Track 4 by trains continuing to Government Center, North Station, or Lechmere. Track 3 is not used as much as the others, as Park Street is not currently a regular terminus, so only trains being short-turned use it. It loops around and turns into Track 2 (a switch allows trains from Gov't Center to reach Track 2 as well). There's also a stub track long enough to hold one car with an inspection pit that connects to Track 3.

With trains serving four different branches, it's rare for more than a few minutes to go by with no trains in the station, and there will often be multiple trains in the station at once.