Basement Layout 2.0 - Mainlines?

@raising4daughters I have a very similar track plan and the curves have not caused any problems. I like the design!

AFAIK, an ”S” curve is where a curve changes direction with the track next to it. As long as there is at least 1 standard length (10” or more) straight track between curves that go in opposite directions you shouldn’t have problems. The straight track allows the cars to straighten out before they get pulled in the opposite direction, reducing the force on the wheels.

Except for the yard and sidings, that is almost an exact duplicate of my layout. I eliminated the "S" curves coming out of the curve. The outer curve is a stretched O-36 and the inner is O-31. Traditional sized Legacy steamers and diesels are not a problem and I recently picked up the LionChief + 2.0 Big Boy and it runs flawlessly.

@Chris1985 -thanks for the pics. Yes, our layouts look remarkably similar. My RR Track file shows a second level like yours.  Appreciate the feedback that the curves shouldn't be a problem.

@Richie C. - I like your layout. Great minds think alike   How wide is your layout from the yard on the left to right side of the U-shaped mainline.  I've got 13-1/2' to deal with width-wise, and that's wall-to-wall, so I have to consider reach from the center of the U.  I'm wondering if you've got the ability to walk to the left of your yard where I have a wall in the way.

I'm also using O27 tubular track, and that limits my options on curve diameters. I don't want to have any 27" curves on mainlines. I have some 34" Marx curves laying around, but they're pretty rusty and ugly, so my real low-end limit is 42".  I could go 42" and 54" and get rid of the 72" on the right side of my U, but I'm not sure that would free up enough space for a complete turn around AND a nice yard with the width of yours.

Guessing you've got a good 8'-10' in width just on the left side of your layout.

Love it!