Before revision: The Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines are deep-level tube lines, using smaller trains that run through two circular tunnels with a diameter of about , lined with cast-iron or pre-cast concrete rings, which were bored using a tunnelling shield.
After revision: The Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines are deep-level tube lines, using smaller trains that run through two circular tunnels with a diameter of about , lined with cast iron or precast concrete rings, which were bored using a tunnelling shield.