These grades aren’t very steep for model trains, but they are steep grades for real-life trains. In real-life railroading, there are three classes of grades: 0.8 percent to 1 percent is “light grade,” 1 percent to 1.8 percent is “heavy grade,” and anything greater than 1.8 percent is “mountain grade.” Because of this limitation in real-life trains, some builders of prototypical model railroads will ridicule any grade steeper than 2 percent, calling them “toy train” layouts. Maximum grade is frequently dictated by available layout space. The implied requirement is that if you are building a small layout it should be flat. But why not a mountain grade railroad over a flat oval or figure eight? With model train track, grades can also be used to make a layout more visually appealing. But interesting layouts frequently pass one track over another on bridges or trestles. And gaining sufficient height for an over/under on a short model railroad layout is where grades become a challenge. Manufacturers of trestle piers and tunnel portals generally exceed this dimension sufficiently to take into account the height of the rails for most model railroad tracks. However, there are numerous cases where tunnel portal products don’t have sufficient clearance for models of modern locomotives and cars. Pantographs on electric locomotives increase clearance requirements, too. Remember that the track must also descend back to its starting level, so this length of the grade is required on each end of the bridge. The diagram shows N scale crossovers layouts for 2 percent and 4 percent grades. Ascending tracks are in green and descending tracks are in red. The 2 percent grade layout requires more than 6 yards of length for the layout. The diagram shows N scale figure eights with the grades split. The 4 percent grade layout now has a length of 3 yards. The blue outer curves are the midpoints of the grades. You could further shorten the layout by making the curves part of the grade. However, curved grades have additional considerations. An example is an 11-inch radius curve with a 4 percent grade in N scale. An Athearn consolidation class locomotive would pull nine of its Overton passenger cars over this curved grade with no difficulty. If you made an 8.5-inch radius curve with a 4 percent grade, the consolidation would only pull five of its cars over this tighter turning grade. This grade is 1 inch high, half the N scale over/under height. In the Steam Era, it was not unusual for railroads to have “helper” locomotives standing by to be added to trains at steeper grades. While modern prototypical diesel trains usually put all the locomotives at the front of the train, some modelers put locomotives in the middle of a train.
