Gradients.

Having been brought up on 'British 'gradients ( 1 in 264 etc.) I have difficulty with the American system. Is it the height expressed as a percentage of the length, ie.- 1 % equals a rise of one over a distance if 100 (1 in 100)and 0.5 % equals 1 in 50 ?

Right - Thanks!

(I'd been reading an article in Trains about Mountain Railroads and without knowing that it did'nt make much sense ! )

Just as we measure grades in percentages, not ratios, we also measure curves in degrees, not radii. For a better explanation on measuring curves (the article is geared towards model railroading, but also applies to the real world), go here: http://www.steamlocomotive.com/model/curve.html