Are my mainlines reasonable?

I only see 2 what I would call "S" curves, and they don't appear to be that  radical. Take 'em slow and see what happens!

Simon

If you do have a problem with string lining, adding weight to get your rolling stock to NMRA standards will help with that.

I think you're fine in terms of s-turns. doesn't seem like you have any real tight ones. Only thing I'd consider is taking at least the inner loop and making it a folded figure-8, makes for a little variety to have trains passing head on in one section, and running side by side in another. Below is the original schematic for my prewar layout. I've currently looking into adding an upper level to get a few more trains going at once.

Keep us posted on your progress.

Tim

Tim - thanks.  I like your layout and will definitely try to include the folded figure-8.  Thanks for the tips. 

Scott

Scott, the only comment I have is to be sure center-to-center distances between parallel tracks in curves is adequate for the equipment you will be operating now and in the future.  Good luck.

Looks pretty good. A couple of spots look like the lines are too close together, but that's probably not a problem with O-27/O-31 equipment.

As an aside, don't worry about the basement. You'll get it back when they go off to college.

Trouble with a folded loop, with an at-grade crossover, is that you can't easily run 2 trains.  If you have room for grades, an over-&-under crossover would be better.

On your sketch, consider a connection between the end loops via a swing-up bridge.  On a thread somewhere else I depicted a swing-up bridge across the acces to my workshop, using microswitches to throw switches when bridge is up, to prevent collisions between trains and concrete floor.

Matt - thanks.  Yes, I wasn't overly precise on the closeness of the tracks. Is there a guideline for distance between tracks when using traditional-sized equipment. My longest cars are O27 passenger cars.

Oddly enough, two of the girls are in college already and one is a high school junior. They have friends over periodically and want more basement space for TV watching etc.  They're willing to bunk up when sleeping since that's what they do at college.