extended to Kyzyl-Arvat (today's Serdar), by 1886 had reached Chardzhou (today's Turkmenabat). In 1887 a wooden rail bridge was built over the Amu Darya, and the line was continued to Samarkand (1888) and Tashkent (1898). The rail line connecting Mary to Serhetabat was completed in 1898, and the train ferry between Kislovodsk (Türkmenbaşy and Baku began operating in 1905. Rail service in Turkmenistan began as part of Imperial Russia's Trans-Caspian Railway, then of the Central Asian Railway. After the collapse of the USSR, the railway network in Turkmenistan was transferred to and operated by state-owned Türkmendemirýollary. Rail gauge is the standard Russian- and Soviet 1520 millimeters. The total length of railways is 3181 km. Only domestic passenger service is available, except for special trains operated by tour operators. The railway carries approximately 5.5 million passengers and moves nearly 24 million tons of freight per year. The Tejen-Sarahs-Mashhad railway, built in 1996 by Turkmenistan and Iran, has become a vital freight link of Central Asian-, Russian-, and European rail systems with South Asia and the Persian Gulf. In 2006 the Trans-Karakum Railway, a direct link between Ashgabat and Dashoguz, halved travel time between the southern and northern borders. The Kazakhstan-Turkmenistan-Iran railway link, part of the North–South Transport Corridor, is a -long railway line connecting Kazakhstan and Turkmenistan with Iran and the Persian Gulf since 2014. It links Uzen in Kazakhstan with Bereket and Etrek in Turkmenistan and ends at Gorgan in Iran's Golestan province. In Iran, the railway connects to the national network, including seaports on the Persian Gulf. The project cost an estimated $620 million, shared by the governments of Kazakhstan, Turkmenistan and Iran. This link of the North-South Transnational Railway runs 137 km in Kazakhstan, 470 km in Turkmenistan and 70 km in Iran. Work in Turkmenistan commenced in Bereket in December 2007 and in Kazakhstan in July 2009, and was completed in late 2014. In late 2016, a railway line from Kerki south to Ymamnazar on the border with Afghanistan and beyond to Aqina in Andkhoy District was opened. It is expected to become part of a railway corridor through northern Afghanistan. This line was subsequently extended to Andkhoy. In February 2018, the existing rail line between Serhetabat and Torghundi in Afghanistan was restored to service. This line is planned to be extended to Herat, where it could potentially connect to a rail line under construction from Khaf,