The Kiev Metro is a relatively simple system – three independent metro lines running across the city, with passengers changing between them at one of three interchange stations. However trains do have a way of making their way between the lines, using hidden tracks that passenger services do not use.
Known as «Служебная соединительная ветвь» (service connecting branches) these single-track tunnels connect three Kiev Metro lines via a series of tight curves – their 150 metre radius is far shaper than the usual 300 metre minimum radius – resulting in a 40 km/h speed limit, with a recommended speed of 18 km/h.
The first connection to open was «ССВ-1» in the mid-1970s, linking Khreshchatyk (Хрещатик) station on line 1 with the under construction line 2 at Maidan Nezalezhnosti (Майдан Незалежності) station; followed by «ССВ-2» in the late-1980s, connecting the new line 3 at Klovska (Кловська) station to the rest of the network via the «ССВ-1» tunnel.
Trains using the connecting tunnels include:
- transfers to the carriage repair plant at «ТЧ-1» Darnytsia from other depots;
- delivery of new trains to «ТЧ-2» Obolon or «ТЧ-3» Kharkivske depots;
- transport of new rail from the welding workshop at «ТЧ-2» Obolon depot;
- until 2007, line 3 had no depot so trains were serviced at «ТЧ-2» Obolon depot;
- until 1988, line 2 had no depot so trains were serviced at «ТЧ-1» Darnytsia depot;