I use Maggs Re-rail portal along with pguy's Portal Timetable rule for interchanges. It will emit a string of cars at the time you want without an engine. They appear on the interchange track, that piece of track on which both railroads have joint rights. I then pick them up with my switcher. Dropping off cars is a bit of fun because you have to drop kick them into the interchange track (portal) or you will loose your engine. I find if I get up to a speed of 20mph pushing the string of cars, uncouple the engine and cut the throttle, the cars roll into the interchange track and I reverse and go back to the yard. This allows more than one interchange operation per session - like one in the morning and one in late afternoon.
One could also use AI to bring the foreign road train onto the route and do the drop-off and pick-up, but I have had problems with that in the past.
I think once you start to use portals, you will find there are many possibilities. Do you have any grade crossings with other railroads? This always makes for an interesting operations feature. There is a diamond crossing rule that takes care of the signaling. My road has 9 grade crossings with foreign roads, all of them with active cross traffic.
