Park Street is a bi-level station, with the Green Line running on the upper level and the Red Line on the lower level. The Green Line has four tracks numbered 1 to 4 (north to south). Tracks 1 and 2 serve an island platform for westbound trains. Tracks 3 and 4 serve an island platform for eastbound trains, with an additional side platform serving Track 4. Track 4 is used by all eastbound through trains; Track 3 is only used by trains terminating at Park Street, as it loops to rejoin Track 2. Both island platforms have headhouses and fare control areas on their northeast end; the westbound platform also has a headhouse at its southwest end. A sub-passage connects the middle of the three Green Line platforms. A passage from the eastbound side platform leads to a small fare lobby under Winter Street, with stairs to the surface and the Winter Street Concourse to Downtown Crossing.