I am in love with the Back to the Future III advent calendar. It's lovely! Now I need to clear some more shelf space to fit all the fun backdrops.
Anyway, the train wheels snap on just fine, but they do not automatically fit on playmobil train tracks.
playmobttfiii_14 by
Andy Jones, on Flickr
So I put two track pieces side by side and interlocked the ties, like a zipper, and the distance between the left rail lines up with the left rail on the other track, so much so that if you had a lot of parallel track lined up, it rolls smoothly!
tracks_01 by
Andy Jones, on Flickr
Here's another angle
tracks_02 by
Andy Jones, on Flickr
But for displaying on your shelf, just get two pieces of track next to each other, and it'll rest on it just great! You can't even tell in the top photo that there are two rails there. But it works!