@Kiarev53, and by way of example: The real-world D&RGW mainline west of Denver has, as best I can tell, the single, sharpest curve of any mainline track on the entire system--a single sixteen degree curve in Burns Canyon. There is a speed restriction through the whole canyon of 20 mph (in both directions).
A sixteen degree curve has a radius of ~360 feet, or ~27 inches in N scale. This also the sharpest curve listed in the Rio Grande's curve vs. speed elevation table, so it's a safe bet there are no mainline curves sharper than this one anywhere else on the system.
The elevation chart lists (1/2" increments) allowable speeds of 15 mph for elevations of 1/2" or 1", 20 mph for elevations of 1 1/2"-3 1/2", and 25 mph for elevations of 4"-5" for a sixteen degree curve (5" is the maximum elevation listed for D&RGW track, even though other railroads sometimes go higher).
So why doesn't the Rio Grande bank that curve 4"-5" (25 mph) instead of only somewhere between 1 1/2" and 3 1/2" (20 mph)? Because there are other considerations for combination and/or reverse curves (reverse curves--"S curves"--change direction from right to left, or the other way 'round), and in this case the next curve (heading west) does indeed, turn in the other direction. This matters, because it's not only a need to elevate a given curve for a certain speed but also of coming back down to level (0") from that same elevation. With a reverse, or S curve, it's also necessary to bring the next curve up to ITS selected elevation (the elevation "switches rails") with a similar, gradual transition, and each transition takes a certain distance to make the change--I want to say the allowable change is 1 inch for every 100' track segment (known as a "station" in surveyor-speak), but I'm going on a long-distant memory, so I'm not completely sure about that.
However, and assuming I am right, a transition between a pair of curves, each elevated to 2 1/2" would take two and a half stations (250') for each rail to come back down to level. That would be a total of five stations (500') to affect that change in banking from one curve to the next. A 3" elevation for each curve would take 600', etc.
The transitions are done over a section of each curve known as "easements," where each curve gradually straightens out before meeting the next curve turning the opposite direction (these transitions are also known as "spirals," as they are laid out using mathematical formulas).
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"Very good"/aka "top-notch" model railroad practice is to use easements or spirals at the end of most mainline and even branch line curves, and even though our easements might be shorter (in the same way our curves are usually much sharper), some sort of transitions will also allow a given banking to come back down to flat and level--elevation zero.
There is more to model railroading elevation/super-elevation of course--there always is--but that's enough for this post.
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