LU plans to invite tenders for the fleet next year, and requires 100 trains each for the Piccadilly and Central lines, 40 trains for the Bakerloo Line and 10 trains for the Waterloo & City Line.

These will be the first air-cooled trains for the so-called Tube lines which have a very restricted loading-gauge. Wide inter-car gangways will enable passengers to walk through the trains to improve passenger distribution and provide more capacity compared with the existing trains. Coupled with new communications-based train control (CBTC) on each line, LU expects to increase capacity substantially.

The greatest increase in capacity will be on the Piccadilly Line where a 60% rise is expected by running at least 33 trains per hour by 2025. Capacity on both the Central and Bakerloo lines is forecast to rise by 25% with 33 trains per hour during peak periods on the Central Line by 2030 and 27 trains per hour on the Bakerloo Line during the peaks by 2033. Finally, LU expects to achieve a 50% capacity increase on the Waterloo & City Line by 2032 with 30 trains per hour running during peak travel times.