The Faroe Islands is served by an internal transportation system based on roads, ferries, and helicopters. As of the 70s, the majority of the population centres of the Faroe Islands have been joined to a single road network, connected by bridges and tunnels. There are no railways on the Faroe Islands due to the difficult landscape, small population and the relatively short distances. A tunnel and rail system supplied a NATO radar installation, now decommissioned, once existed on a mountaintop in the southern part of Streymoy Island. There is an extensive bus network, with red and yellow Bussleiðin town buses serving Tórshavn and Klaksvík respectively, and blue Bygdaleiðir (which means "village route") buses connecting the rest of the islands. Most buses are modern and were built by the Volvo company. The network of blue Bygdaleiðir rural buses (as well as the ferries) is operated by Strandfaraskip Landsins on behalf of the Faroese government, which provides subsidies. The principal route is Tórshavn-Klaksvík (via the new Norðoyatunnilin tunnel), but other bus routes also serve most villages. Although individual buses are generally owned by individuals or small companies, the timetables, fares, and levels of service are set by Strandfaraskip Landsins and the government.