Transport for LondonRolling stock
1996 stock
Rolling stock cannot be transferred easily from one line to another, although it has been done in the past.
For instance, the 1983 stock introduced to the Jubilee line displaced 1972 stock to the Northern line. Northern line 1959 stock then moved to the Bakerloo line which meant 1938 stock could be withdrawn.
Different lines have different sized tunnels. The original City & South London Railway tunnels were 10ft 2in (3.1 metres) in diameter. Later lines saw the internal tunnel diameters rise to 3.6 metres, and up to 3.8 metres with the Victoria line.
S stock
Besides diameter, other physical features such as curvature and platform length mean that rolling stock can usually only be used on one specific line.
For example, the Central and Victoria lines platforms are 400ft long and have different Automatic Train Operation signalling systems. Most other Tube platforms are only 350ft.
The platforms on the western part of the Circle line were too short to take the District line D78 Stock. As part of the upgrade plan, these platforms are being lengthened to take the S7 trains that will run on both the Circle and District lines.
As the Underground is modernised, the signalling systems are being updated to provide automatic train protection (ATP) which requires specific equipment on board the train to communicate with the signalling system. Only trains fitted with the correct equipment can operate on a line with ATP, another reason why trains only operate on a designated line.
Tube stocks are usually identified by the year in which delivery was scheduled. Sub-surface stock has a letter followed by two numbers. This indicates the year it was first delivered.
'D' stock
Most rolling stock lasts around 40 years. Major refurbishment can prolong life by another 10-15 years and costs around a sixth of the cost of a new train.
A Stock (A60/62) was initially introduced in 1960 and so has been in passenger service for more than 50 years.
Further reading: Underground Train File - 1933-1959, by Brian Hardy. Published by Capital Transport 2001.
