While the real railroads bank their curves I would advise against it on a model railroad, particularly using small radii on a steep grade. The physics is far different for model trains than real ones, and long trains can roll over on banked curves. I t was a well known hazard on my grandfather's layout, where one 24" radius curve was unintentionally banked. Unless you were very careful starting a long train on this curve, it would roll over. Since the curve was near the entrance to a yard, trains often stopped there. And to make matters worse, much of the curve was in a tunnel which meant a trip under the layout to reach up inside the mountain to retrieve the derailed cars. We didn't have that problem on the unbanked curves, or any of the unbanked ones on subsequent layouts our family has built over the years.