The railway that conntcts Russia and China is of two different gages. When you reach the border, you don't change coaches. Oh no! You change wheels or trucks to be more precise.
The coaches are un-coupled and moved to a huge building that can hold 40 or 50 coaches at once. There, the pins which hold the coach and trucks together are removed and the coach is jacked up. A new set of trucks is rolled in on a parallel set of tracks, the coach is shifted the foot or so necessary for re-alignment of holes, lowered into place, the locking pin is inserted and the train is slowly reassembled.
The whole process takes anywhere from one to five hours. We went through it twice last summer. Once we had to leave the train but the second time we were allowed to stay aboard.
The gages are different because the Chinese were afraid of a Russian invasion when they first began building a national railway system. They didn't want the Russians to be able to use the Chinese rail roads to move war materiel.
Hence, the difference.

troll