I'm planning a new layout and it will have a hidden yard and loop accessed by a helix. Trains will be made up on the upper visible level and held in the yard-loop until needed so I don't need to handle the trains unless there is a problem. I would like some thoughts on the separation needed between the levels. I need at least 6 inches to accommodate switch machines, etc. but this seems to small to accommodate a hand trying to get at a derailed car. I realize that this is rather a personal thing like layout height but some practical advise would be appreciated. Once I get this level built I can experiment with a temporary upper level and find a height I like.
Thanks.
Richard Foster