Around four million passengers travel on the London Underground each weekday, which equates to well over one billion people a year.
These passengers expect a reliable and efficient service. And to help meet their demands, the Tube stock is constantly being refurbished and replaced.
LU’s Tube Improvement Plan, costing some £10 billion to 2017/18, is intended to increase capacity and provide a better travel experience for passengers. Over the next decade there will be new signalling systems and control centres, old equipment will be replaced, key stations will be rebuilt and refurbished, and new rolling stock will be introduced.
The brand new fleet of S-Stock trains makes up a £1.5bn chunk of that plan. Being rolled out on all sub-surface lines (it has already replaced the A-Stock), the new fleet finally brings much-desired new characteristics to the Tube, such as air-conditioning.
But LU cannot replace all trains overnight, and S-Stock will only replace trains on sub-surface lines. Travel around the Tube system, and you will therefore still be able to see nine different types of Tube stock operating - three sub-surface (C-Stock, D-Stock and S-Stock) and six deep-level (designated by the year it was intended to enter service).