Add train load/unload interrupt condition(s)

It would be nice if there were a way to add an interrupt condition to a route where a train would stop it's current action and continue to the next objective. IE I want a train to fully load at station 1, then unload 50% at station 2 even if it can hold more and unload the final 50% at station 3, then start again. This would allow you to create routes where you divide the cargo based on the number of destinations.