British railway system is the oldest in the world and the first locomotive-powered public railway opened in 1825. Most of the tracks are managed by Network Rail, which in 2014 had a network of 15,753 kilometers of lines. with standard gauge, of which 5,268 kilometers were electrified. These lines are single track, double track and in certain sections of quadruple track. Also, some cities have separate public transport systems on rails (including the long and historic London Underground). There are also several private railways (some of them narrow gauge), which are mainly short tourist lines. The British rail network is connected to that of continental Europe by an underwater rail link, the Channel Tunnel, inaugurated in 1994.