Cross-passage

At the lowest point, a short length of tunnel was driven alongside the up line, with a cross passage, to serve as a sump and pump house for dealing with any accumulation of water.

The smaller cross-passages between the two running tunnels are for use in emergencies. Unlike the main tunnels being excavated by Tunnel Boring Machines (TBMs) Florence and Cecilia, they are dug using remotely controlled mini-excavators.