The Baikal–Amur Mainline (Baikalo-Amurskaya magistral', BAM) is a 1,520 mm (4 ft 11 27⁄32 in) broad gauge railway line in Russia. Traversing Eastern Siberia and the Russian Far East, the 4,324 km (2,687 mi) long BAM runs about 610 to 770 km (380 to 480 miles) north of and parallel to the Trans-Siberian railway. 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-na-Amure and finally reaches the Pacific Ocean at Sovetskaya Gavan. There are 21 tunnels along the line, with a total length of 47 km (29 mi). 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 1,469 km (913 mi) 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. The original section of the AYaM connecting the Trans-Siberian at Bamovskaya with the BAM at Tynda is also referred to as the "Little BAM". During the winter the only passenger trains go from Moscow past Tayshet and Tynda towards Yakutsk. Travel time from Tayshet to Tynda is 48 hours.