Thanks Dave, I went back and looked at those plans. I assumed since there were no reverse loops on the lower level trains would always run counter clockwise.
18" is better than 15" if the space works. I do not like the top of the cars and engines to be higher than eye level. So that says the top of the trains must be less than 60". Subtract 5" for the roadbed, track and train height the table height is 55" off the floor. If the bottom level is 40" high and the thickness of the upper deck structure is 3" (a 1"x3" plus a 1/2" plywood) that leaves 15" clear between the 2 levels. In my world the lower level would have to be 37" high to get 18" clear space. Were me and my operating friends all 6'-4" then I could make the layout higher!!!
This is mostly personal preference. As long as the owner is satisfied then all is well.
