Model trains don't have to stay on level ground. Adding a grade or changing elevations can add a lot of interest to any layout. How steep is too steep?
Plan your grades to make the most out of the track and not overtax your locomotives. Calculating grades is easier than you think.
Model or prototype, the severity of a grade has a major impact on the operations of the railroad. Grades determine the length and weight of trains, the number and type of locomotives assigned and the speed limit. Railroad engineers strive to keep grades to a minimum, but they are an unavoidable part of life in most places in the world.
Calculating the Grade
Grades are written as a percent, with the amount of vertical rise divided by the length of horizontal run. In the real world, these numbers can be quite large. On a model railroad, we can think in terms of inches and feet. A 2 percent grade for example would climb 2 inches in every 100 inches (or 1 inch every 4 feet, 2 inches).
So just what is the steepest grade a train can climb? As usual, there is no one right answer to this simple question. It all depends on the prototype. A mountain logging railroad for example might have grades of 5 or 6 percent or more. Geared locomotives, short trains and slow speeds can easily conquer that challenge.
For a heavy mainline, a 1.5 to 2 percent grade would be considered steep and may even require helper locomotives. Mainline grades in excess of 2 percent are generally considered quite severe. The length of the grade also has a lot to do with things. A 1.5 percent grade that extends for 60 miles will have more impact on the railroad's operations than a 2.2 percent grade that is only 1/2 mile long. A train has a lot of momentum - enough that it can help power a train up a short grade without great difficulty.
Because the method of calculating a grade is the same for both model and prototype, the same standards generally apply. Since most model trains are short by prototype standards, a 4 percent grade, or even slightly greater, is still quite steep but manageable for most layouts. Grades of around 2 percent are much more realistic and manageable but will still impact train speeds and engine capacity. Grades of 1 percent or less can be handled without any concern.
Curves and Grades
In addition to the length and percent of a grade, curvature within a grade also has an impact on operations. Curves increase the friction between wheels and rails, consequently it will be both harder to pull a train up a curving grade and easier to bring it down.
Adding curves to a grade on a model railroad can help provide a longer run in a smaller footprint and therefore actually reduce the percent of grade. Too many curves, excessively sharp curves, or frequent reverse ("S") curves can create problems. The combination of sharp curves and steep climbs can prove too much. Try to achieve a happy balance between the two. Unlike grades, minimum curve radius varies between scales.