It doesn't have to be complicated though, and it also doesn't need additional information. The trains could simply be "parked" at terminus stations, and when a

It doesn't have to be complicated though, and it also doesn't need additional information. The trains could simply be "parked" at terminus stations, and when a train is scheduled to depart in the other direction, check if a train is available at the station - if yes, use it, if no, create a new one.