Parcel 1 Pano of Big Dig before removal of highway. Taken on Causeway Street, near the current Boston Garden - previously called the Fleet Center. You can see the green structure of the elevated Central Artery (as called I-93 and Rt 3). The brown steel beams are holding up the elevated highway because the construction of the Big Dig tunnels is in full swing below. The brown steel is supported by the outer concrete slurry walls that go down to bedrock and form the walls of the eventual highway tunnels.