Determining curvature of a single piece of sectional track

Jim, I too was not blessed with the math gene. My suggestion would be to make a template of the curve on paper or some heavier gauge material. Then you can move it where you want. I did several half curves of various curve degrees. So much easier than doing the math. Gives you an instant visual.

Jay

Or you could measure from end to end of the curve and then measure from the midpoint of that line to the midpoint of the curve and calculate the radius.

Take the single piece of track. Measure the length of the outside rail with the curve, not straight across. Take that number times 8 and then divide the new number by 3.14    
Some track manufacturers use the center rail and some approximate.  The number 8 represents the number of pieces of track used by Gargraves to complete a circle of there smaller diameter track systems

Thank you all very much. Good news and bad news. The track curvature is 0-42, but I won't be able to use a curved switch for what I want. A left hand 0-42 will do the trick, though - which creates some opportunities.