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.