The technical difference is that metros have dedicated tracks and sufficiently frequent services that you can just turn up and go. In Melbourne (and Sydney), t

The technical difference is that metros have dedicated tracks and sufficiently frequent services that you can just turn up and go. In Melbourne (and Sydney), tracks are shared in complicated ways by many lines and other traffic (regional, long distance, even cargo) so any issue somewhere cascades in complicated ways, and frequencies are metro-like only in the densest corridors.