Known colloquially as 'the Drain', it was one of the first lines we focused our efforts on, and the work we carried out has made it faster, more reliable and easier to use.
It may be a short line, but it's a busy one, and by improving reliability and moving more trains, more quickly we were able to create more capacity - or room - on the line.
Following the upgrade capacity was increased by a quarter, which means we can carry about 4,000 more passengers an hour.
We also made journeys 12 per cent faster between Waterloo and Bank.
At peak times, Bank is one of the most congested stations on the Underground. It's also a complex one as it's interlinked with nearby Monument.
To help remove some of the bottlenecks, we're refurbishing or replacing all of its 15 escalators. We'll also be introducing a one-way system in parts of the station, which should help ease congestion while the work's being done.
We aim to keep Bank open throughout the works, but it's a big, complex project, so please bear with us.