The Albula Tunnel is the centrepiece of the Albula Railway, which forms part of the Rhaetian Railway network, in the Canton of Graubünden, Switzerland. With its maximum elevation of 1,820 m (5,971 ft) above sea level, it is, after the Furka Tunnel, the second highest alpine tunnel in Switzerland, and has a mountain overlay of up to 950 m (3,117 ft).
The northern portal of the tunnel is at Preda, in Bergün, and the southern portal at Spinas, in the Bever valley. At a total length of 5.865 km (3.644 mi), the tunnel connects the Albula Valley with the Engadin Valley, and, in so doing, passes under the watershed between the Rhine and the Danube a few kilometres west of the Albula Pass.
The tunnel serves both passenger and freight traffic. The Glacier Express passes through it daily, as do car transporter trains operating between Thusis and Samedan.
The construction of the tunnel caused unusual problems. The cold, 6 °C, water outflows transformed the already fractured rock into a pulpy mass, regularly clogging up the shell of the northern tunnel lead (or adit). At the same time, a strong water source above the northern tunnel portal dried up. The water streaming in at 300 L per second had to be painstakingly diverted with pipelines. As a result, construction virtually came to a standstill: in the ten weeks from May 1900, only two metres of tunnel were driven. These difficulties could not be overcome by the head construction contractor Ronchi & Carlotti, which went into bankruptcy.
From 1 April 1901, the Rhaetian Railway took the construction work into its own hands. With the use of a bonus system, it was able to regain part of the lost time. At 03:00 hours on 29 May 1902, the breakthrough of the two tunnel leads was achieved, at a point 3,030.5 m (9,942.6 ft) from the north portal, and 2835 m 2,835 m (9,301.2 ft), from the south portal.
The tunnel cost 7,828,000 Swiss francs to build. A total of 1,316 people were employed in its construction. Overall, there were 16 fatal accidents involving tunnel workers, and at the Preda station there is a stone memorial to commemorate the victims.
In June 2009, the Rhaetian Railway announced that it was conducting investigations into either fundamental modernisation or reconstruction of the tunnel.