Under which mountains are the railway tunnels being built for the Alp-Transit project?
The most dense rail network in Europe of 5,063 km (3,146 mi) carries over 350 million passengers annually. In 2007, each Swiss citizen travelled on average 2,258 km (1,403 mi) by rail, which makes them the keenest rail users. The network is administered mainly by the Federal Railways, except in Graubünden, where the 366 km (227 mi) narrow gauge railway is operated by the Rhaetian Railways and includes some World Heritage lines. The building of new railway base tunnels through the Alps is under way to reduce the time of travel between north and south through the AlpTransit project.
Important geological concepts were established as naturalists began studying the rock formations of the Alps in the 18th century. In the mid-19th century the now defunct theory of geosynclines was used to explain the presence of "folded" mountain chains but by the mid-20th century the theory of plate tectonics became widely accepted.