Baikal–Amur Mainline  The Baikal–Amur Mainline (, , , ) is a broad gauge railway line in Russia. Traversing Eastern Siberia and the Russian Far East, the long BAM runs about 610 to 770 km (380 to 480 miles) north of and parallel to the Trans-Siberian Railway. The BAM was built as a strategic alternative route to the Trans-Siberian Railway, especially along the vulnerable sections close to the border with China. The BAM's costs were estimated at $14 billion, and it was built with special, durable tracks since much of it was built over permafrost. Due to the severe terrain, weather, length and cost Soviet premier Leonid Brezhnev described BAM as "the construction project of the century". If the permafrost layer that supports the BAM railway were to melt, the railway would collapse and sink into peat bog layers that cannot bear the railway. Over the last years the number of reports about climate change and damage to buildings and infrastructure as a result of thawing permafrost have increased. The BAM departs from the Trans-Siberian railway at Tayshet, then crosses the Angara River at Bratsk and the Lena River at Ust-Kut, proceeds past Severobaikalsk at the northern tip of Lake Baikal, past Tynda and Khani, crosses the Amur River at Komsomolsk-on-Amur and finally reaches the Pacific Ocean at Sovetskaya Gavan. There are 21 tunnels along the line, with a total length of . There are also more than 4,200 bridges, with a total length of over 400 km (about 260 miles). Of the whole route, only the western Tayshet-Taksimo sector of is electrified. The route is largely single-track, although the reservation is wide enough for double-tracking for its full length, in the case of eventual duplication. The unusual thing about the railway is that it is electrified with a 27.5 kV, 50 Hz catenary minimum height at 6.5 metres above top of the rails to suit double-stacking under the overhead wires on the Russian gauge tracks, which requires rolling stock to be modified for service on the railway. At Tynda the route is crossed by the Amur–Yakutsk Mainline, which runs north to Neryungri and Tommot, with an extension to Yakutsk opened in 2014, and now extension to Magadan under construction.