Because they have often replaced push/pull trains, their shorter journey times, such as on the Müglitzbahn, have made greater passenger numbers.
The wires were put up as electric trains began to replace coal-fired trains in the early 20th century.
Other refurbished trains moved to Line 4 to replace unrefurbished trains that were being retired.
In the event of buses replacing trains, only one service in each direction runs, usually in the late afternoon.
When the Metrolink took over services of the line, the third rail was lost, and trams replaced trains in 1992.
S Stock is replacing trains on the Hammersmith & City line.
The 906 bus uses the western side of the station on Curtin Avenue but only operates to replace trains during line maintenance closures.
Buses replaced trains in many areas, including all east coast services in Scotland.
On the 1 line, shuttle buses will replace trains between Dyckman and 168th Streets in Manhattan.
The X1 was based on the SJ X6 taken into service in the 1960s, that had replaced locomotive-pulled trains.