[jemmyw]

That's not quite true. The original signals would let a train into the cross over block when no station lines were available because they didn't have that pass through. Depending on the layout it would either get stuck or end up heading in the wrong direction. Pre-signals could solve it but they weren't in the original.

[TylerE]

You just put a signal at both ends of the passing loop. Just the way they’re signaled in real life - one signal to authorize a train into the loop, one to authorize movements out of the loop.

Path based signals (nor pre-signals for that matter) didn’t exist in plain original TTD and constructing such track layouts was easy and straightforward.