Designing a new arena provides its own challenges, but shoehorning a multifunctional arena next to an adjacent active arena, two highways, a river, bridging an active train terminal and over subway tunnels, the planning, phasing and engineering become paramount. The TD Garden was designed as a much-needed upgrade to the old Boston Garden and North Station, which were modernized and folded into the new building with less than 2 feet to spare on each side in which to construct the facades.