Mystery Tunnel Recon

During an all night subway tunnel exploring spree we came up for air where one tunnel ducks into another. Parallel to this tunnel is a curiousity I’ve always wondered about: Why is the right of way wide enough for 5 tracks when there are only 2 in use?

Was there a second tunnel at this location that has been sealed up for decades?

The puzzling evidence suggests there may indeed have been one, though the stark reality is that if it exists, it’s sealed up tight.