Re: Maximum grade for NG RR lines?

In distinguishing NGRR grades from roads, you might also look at a couple of other factors. First is curvature. Most NG lines did not have many curves above 33 degrees or 175 ft radius (with a couple of noteable exceptions) whereas roads often have curves as much as twice that sharp with a radius less than 100'.

The other thing that you might use is the amount of cut and fill that you can find. Logging roads basically run on the ground with minimal cut and fill. Any main haulage railroad line, even for hauling logs, or mining will have some cuts and fills and other grading. Only the most temporary of spurs will not have a bit of grading.

Last but not least, many later logging roads were actually built on the old rr grades as the rr had the best route, and unfortunately that complicates matters.

You did not say whether you are actually looking in the field, using old maps or what ever to locate your lines, but other than very old maps, pre WW-2 USGS maps, etc the best modern tool is LIDAR which cuts through the vegatation and allows you to see terrain with as little as 2' elevation differences.

I use all of these thoughts, and tools in looking for abandoned logging RR grades in western Louisiana and east Texas.

I hope that this helps.