Matthew, You PM'd me this... Lessee, where do I start... I don't think you can do an over/under. The barest, barest, barest minimum you might be able to get away with is a depth of 3.5 inches between top of plywood and bottom of glass (or lowest support structure of the top of the table). See picture 1 for an illustration of this. This is actually a section I drew for the round table and just kept using it for the others. You need to keep in mind that the blue line across the middle is the elevation I chose to locate the crossing at. The overhead line rose 3/4" above that and the under line dropped an inch resulting in respective grades of 3 and 4%. In a table of this size, 4% is nothing really because you won't be pulling trains of any great length and any locomotive you throw on there should have no problem. When calculating the height you think you will need, don't forget to think about the height of the cork, ties, and rail. With this said, I don't think you can do an over/under in the space you have unless you can figure out how to drop the bottom of the table down to around 4". Check, check, and triple check your numbers. The second picture, is what I think your table looks like from the dimensions you gave me. Hopefully that is self explanatory but if it's not, ask and I will explain any confusion. The cyan dimension lines are almost unreadable. Sorry 'bout that. Now your glass depth is only 17" so if you want a circle of track within that range, you will have to go with an outside radius of something like 8.5". 9-3/4" is the smallest recommended radius in N scale however, I have gone with 7" (actually 6-13/16"). It works but it is really tight and you can not go with anything bigger than a double axle diesel or smaller (test your loco's on something this small before you actually nail it down). If you went with the exact plan I did in my longer coffee table, yours would look like this... I think you could probably stretch that out a little (vertically and horizontally). If you stretched it vertically, you could reduce that minimum radius a little but then you would have track underneath the lip of the table where you can't see it under the glass. Keep in mind that this is just an example of something you could do. When I did this table, I was looking to cram as much track as I could in that space. It worked out to something like almost 21 linear feet of track if I remember right. If you did not want to do a folded dogbone, you could probably go with something much simpler and have a minimum radius closer to 8 or even 9"s. Let me know what your thoughts are. Hopefully this will at least give you some ideas.