The Gotthard Base Tunnel is the world's longest and deepest traffic tunnel, as was the original Gotthard Tunnel at its completion in 1881. It consists of two single-track tunnels, connected by 178 cross-connections. There are two emergency stations in each tunnel, each connected to the corresponding opposite-tunnel emergency station. These stations are equipped with water supplies to refill firefighter and rescue trains. One (Porta Alpina) was proposed as a 800m deep rail station, but the proposal was rejected on both economic and technical grounds. The completed tunnel was handed over to the Swiss government by AlpTransit Gotthard on 31 May 2016. It was formally opened in a ceremony the next day, during which the tunnel was conveyed to its operator: Swiss Federal Railways (SBB CFF FFS).