Realtrax O-54/O-72 layout featuring a double mainline and bridge/trestle track over a ravine

Nice, but to avoid reverse-turns, you could set up the cross-overs in left-right/right-left configurations on the ends of the inside loop. 

"avoid reverse-turns, you could set up the cross-overs in left-right/right-left configurations on the ends of the inside loop. "

What?

Basically, in the corner of the inside loop, you replace the curve with a turnout. The straight leg goes into the curved leg of the turnout placed on the outside loop. This prevents a reverse curve you get from curve-replacement turnouts -- i.e., O-72. The first example is back-to-back left-hand ScaleTrax O-72 turnouts. The second is a left-right style. With Lionel O-72 turnouts, the spacing between the inside and Outside mainline is approximately the same 5.5"; MTH ScaleTrax O-72 turnouts have a short straight section, but a fitter piece can be added to increase the spacing between loops....or not.

Thanks for the example, Matt. That's what I thought you meant, but I wasn't sure.

Edit: I made the change to a layout example from another thread. It wasn't as easy as just substituting the switches. I had to rework several straights to make things fit and it still needs more work. It sure looks better though.

makes sense now

Ah..the perennial missing ingredient..the gauntlet track. This ( gauntlet track ) is going to be my next experimental project as I like the overall concept of your plan. One thing for sure, it was clear what your post was about by way of the title.

Thanks for the education AGHRMatt! I learn a few things every time I get on here. Problem is I sometimes stay too long learning more!  Now if I could just figure out how not to 'foul' (or what ever the proper term is) the main when trying to create a small yard to park and shuffle stuff around in? Have seen a few posts on the subject, but still too dense (or would that be sparse?) for it to fully soak in.

No problem. While you can technically run 3-rail trains through a reverse curve because the couplers are truck mounted, I follow the view that "Just because we can doesn't necessarily mean we should." At speed, you get a shift of the trains lateral momentum that abruptly jars everything. In a fixed-pilot/body-mounted coupler environment, a reverse-curve arrangement on all but extremely broad curves can lead to derailments.

Where it gets problematic is you have to tinker around with fitter tracks using sectional track in the way I described above.

BTW, Pro Hobby, like the gantlet track over the bridge. A lot of roads went from dual to single on either side of a bridge -- building a new bridge gets expensive.

Kind of like all those one-lane bridges on so any country roads.

Good idea.  I have reworked the layout to include this modification but with O-54 left and right turnouts. 

Here is a revised layout with O-72 turnouts and all O-72 curves.