Passenger traffic was a minor consideration. The Metropolitaoa of Naples starts underneath the Central Station and has a route-mileage of about twelve. There is a half-hourly service of little trains resembling tram cars, having two classes. The Metropolitano of Madrid has two main lines and a branch line. The Elberfeld-Barmen Elevated Railway, is interesting in the fact, that, instead of running on rails, it hangs from a rail.
Berlin has numerous underground and elevated railways.
Several years ago it built its Stadtbahn, or City Railway. This began as a connecting link between the main lines from east to west, but it was soon extended as a purely local line. The Berlin Underground, or U-Bahn, was opened in 1923. In 1926 the Municipality of Berlin acquired a controlling interest. In 1928, after a working agreement had been made between the elevated and underground railways, the tramways, and the omnibus companies, the three companies were amalgamated and formed into the Berlin Transport Company.