The London Bridge Station (UK) rebuild addressed two main reasons for unreliability - the signalling as you said (some of it was almost a century old, and that's not an exaggeration), and the other things was removing points. Points are tracks crossing tracks and the rails mechanically switching/

Arguably fixing that by building a fly-under (a tunnel under the existing tracks) fixed a huge source of problems for that part of the UK rail network, probably more so than the signalling.