EEB,
The diameter of the O42 circle is 48".
I measured out 14" at the apex from the corner, that is with one side of the track 3/4" from the edge (wall) and the other side 2". If you are at 13.5 now, the O42 would just about fit, maybe with a small piece added to the middle, and not having to rebuild a lot of shelving.
Post some pics!
I did the same in my sons room in a previous house. I went through the top of the closet as a tunnel, and when I got to the window, I used the mth steel arch bridge to cover the span!
The down side, is the littler kids want to put their hands on the trains and actually play with them, let their gi joes ride in the cars and whatnot. Plus the cleaning of the track is kind of a pain. At least vacuum it once a week!
