All the discussion of the track adjusting into a spiral makes sense, but if you eyeballed the result and tried to fit a simple circular curve it would make the apparent degree of curvature less (larger radius) and the apparent delta larger.
No one has offered any theory on why the mark-up to the drawing increased the degree of curvature from 3 degrees to 3d 15'. Surely the layout wasn't that far from design?
reviving this old thread based on a new survey i am working on. we are working along this RR curve as shown in the attachment. Another retracing surveyor (in 1974) has computed the curve radius to be 5730 at CL, I compute 5729.5. These numbers are assumptions that it is a circular curve, does anything else on the RR plat show its spiral? what does the "1d 00' C.R." mean ?
Whenever I've worked along Railroad Right of Ways the Railroad Plats always showed two curve data, a spiral for the center line track and a simple curve for the Right of Way.?ÿ Your samples look like simple curves.?ÿ CR may mean Degree of Curve (Curve of Rail?).?ÿ EC means End of Curve, BC means Beginning of Curve.?ÿ I wouldn't worry about a half a foot of difference on a radius from the 1970's, after all they were out there with transit and chain or rudimentary edm.?ÿ Your measurements are more precise.
reviving this old thread based on a new survey i am working on. we are working along this RR curve as shown in the attachment. Another retracing surveyor (in 1974) has computed the curve radius to be 5730 at CL, I compute 5729.5. These numbers are assumptions that it is a circular curve, does anything else on the RR plat show its spiral? what does the "1d 00' C.R." mean ?
Back in the old days, 1?ø00' curves were assigned a Radius of 5730' for simplicity of calculations. This was used for both Railroad & Highway Curves.?ÿ?ÿ
A circular curve has one radius, the same value whichever way you want to state the degree of curve. If you calculate radius from one of the degree of curve formulas or some approximation you may get slightly different answers, but for gentle curves it takes a fair amount of change in radius to make much difference in the other curve parameters.
The change on gentle curves isn't usually significant. At the same time it takes little effort to recover and express the curve in the terms it was created in. Why would you do it any other way? In the end it will make your decision easier to defend.
The degree of curve is often considered a synonym for a radius, after all a 1 degree curve has a particular radius.
highway or arc curve=5729.58
railroad or chord curve=5729.65
these two numbers are very close hence Charles' 5730' radius for both.
the 1degree C.R. notation means a 1 degree curve radius. IMO.?ÿ(5729.65 or 5730)
On a Highway curve any radius can be calc'd by dividing the radius of a 1?ø00' curve by the Degree of Curve?ÿdesired, i.e. for a 2?ø00' curve - 5729.578/2 = 2864.789
You can't do that with a Railroad Curve. You have to use the formula: R= 50/Sin?«D. (D=Degree of Curve desired)
