It's hard to think in the American single-track-as-default way of mind ;) Trains going both ways on a single track, great way to get accidents, and trouble scheduling.

Here in France single tracks lines are dying or tourist only, most tracks are doubled, and around Paris not a few see 4 or 6 parallel tracks for reasonable distances...

OTOH freight around here has a minimal market share which is a big problem. And focus on high speed means that Express and local trains are underfunded.

Un roi sans divertissement est un homme plein de misères