Board Thread:Questions and Answers/@comment-24850608-20140422164350/@comment-5596770-20140422185222

And..? If your train isn't on a trip, it isn't doing anything...hence it is idle. You can either let it sit there and do nothing, or you can send it to a contractor or friend.

I'm not sure what you are looking for your Internatioal trains to do, but they don't magically give you things. Sending International trains to is intended to complete contracts to gain the rewards for completing the contracts. Sending International trains to friends gives them gold or materials, depending on what you sent them. The expectation is that they will send International trains back to you, otherwise you don't get anything except for some XP. Sending XP wagons to friends actually rewards you with significant amounts of XP, and doesn't cost you anything except the dispatch cost.