I'm going to be building a layout where there's 2 mainlines. The outer mainline at one point goes over the inner mainline. Because of space issues I've had to allocate 327.5" on one ramp and 310" on the second ramp. Both ramps have a maximum of 4% (I've also accounted for transitions between flat and graded track), which I wanted to avoid but couldn't find a way around it. How problematic will it be running trains up and down?
EDIT: I am using Atlas O 3-rail track. One of the ramps is starts on 64.5" of straight track, then goes in a half circle made of O-81 curves, goes straight for 20", then goes over 2 O-81 curve sections and then ends after another 30" of straight track. The other ramp starts with two O-81 curves, straightens for 11.75", goes over four O-81 curves, straightens for 99.25", goes over four more O-81 curves and then ends after 40" of straight track. The largest engine I plan to use on it will be an AC-12 Cab Forward but the average size will be closer to a 2-8-2/4-8-4 for steam locomotives and EMD E7s for diesels. As far as consist size goes, I'm in the mindset of "as long as possible".
