The UK’s London Underground was originally opened in 1863 for locomotive trains. In 1890, it became the world’s first metro system when electric trains began operating on one of its deep-level tube lines.
It is the world’s third longest metro system, spanning 402km with 270 stations across its 11 lines.
Only 45% of the network actually runs underground, mainly in the city centre, with lines in the suburbs mostly running overground.
The network handles approximately five million passengers a day, with as many as 540 trains operating throughout the network at peak times.
With increased usage, the network has undergone a number of extensions and upgrades since it was first opened but overcrowding is a common problem across the network.
According to railway-technology.com