Query about curves

[SAR704]

Just wondering. Do railway curves have like an apex where the radius is the tightest? Or is the tightest portion of the curve a little more continuous, in order to tailor to its length? Not sure if I've asked this before.

IE you have a 30 chain curve. It starts off very gently at say a 6000 metre radius. Then gradually transitions to around 30 chains at the tightest point. Does this section remain at 30 chains on a long curve? Or does it start to transition back immediately? Obviously it would be quicker with shorter curves.

I am wondering whether or not I should place multiple spline points in curves. I can't seem to find an answer elsewhere. This is due to years of using other sims previously that don't feature splines.

Thanks in advance.

 

[TSwenson]

In prototypical practice railroads have a spiral easement into and out of curves, however they tend to be uniform as possible thru the bulk of the curvature. Part of the problem is that rail curves are so often not simple curves, frequently they are segments of multiple radii in a single "curve" around an obstacle. For example in curvature of sixty degrees of arc there may be 3-6 segments of differing radii (as dictated by terrain) in addition each one has to be eased to the the next. There should be a multitude of civil engineering resources for this, but it is definitely in the realm of civil engineering and not something the average person understands or knows how to do.
In Trainz, the program tries to simulate the easement or spiral portions (with a "bezier" curve, as I recall) to account for the fact that like myself most Trainzers aren't civil engineers and probably couldn't correctly and professionally lay out a rail curve to save their souls. Personally when laying our curves in Trainz, I prefer a spline point approximately every 15 degrees of arc or less, but will vary it by 5 degrees of arc based on other factors. That means seven spline points to make a right angle bend (one to start and 1 every fifteen degrees of arc or 6 segments, 6*15=90). One of my favorite tools/tricks is the old "FT" series fixed track assets used as templates to see where things align and provide a good starting point from which things can be adjusted or not (if it looks right don't mess with it). Ill remove the fixed track and replace it with regular splined track but it does make for nice consistent curves. Also the straightening tool is invaluable for making trackwork look good.