Grades and Clearances
for Your Model Railroad
I received a question recently about how to determine how long the track had to be for a 1% grade to reach an elevation of 4 inches. I figured other model railroaders, especially those just starting out, might have similar questions, so I thought I should include a page on this.
The formula to determine this is as follows:
% grade = height/length (ie, height divided by length)
% grade x length = height
length = height/%grade
Another way to say this is that for a 1% grade, you need about 100 inches of track to go up 1 inch.
Thus, if you want a 1% grade to get you to a height of 4 inches, you will need
4/0.01 = 400 inches of track to get there.
400”/12” per foot = 33.33 feet of track which is quite a length of real estate on a model railroad. This might be okay if you have a large enough area available.
If we were to choose a 2% grade, to go up 4 inches, we could do it with 4/0.02 = 200 inches of track, or 16.7 feet, which may be more realistic for most of our layouts.
Loops and Helices
If you have a small layout, you can loop your track around a few times in order to get to that height in a smaller amount of square footage, or you could build or buy a helix, a circular spiral of track that gradually increases to the desired elevation. Helices aren’t very prototypical however and you’d have to figure out a way to hide them on the side or in the corner of your layout. If you have a large enough layout, that usually isn’t a problem. I personally would prefer watching the train climb the grade as it weaves in and out of mountainous landscape rather than hiding this part of the scenery.
Another thing to remember about grades is that the steeper the grade, the more difficulty your locomotive will have hauling a long string of cars up the grade. You may be able to pull 20 cars on a flat track but only 1 or 2 cars (or none in some cases) on a 4% grade. Traction tires may help, or you could add 2 or 3 locos to help pull more cars up the steep grade. If possible, it would be better to have a smaller % grade for better operation.
One other consideration is to use vertical easements at the bottom and top of your grade. In other words, use a smaller %grade at the top and the bottom and the higher grade in between. For example, if you want to use a 2% grade to get from one elevation to another, use a 1% grade at the bottom of the grade, then ease into the 2% grade. Then, at the top, ease back to a 1% grade before leveling out. This way your train can ease into and out of the grade as it climbs. This will improve operation significantly and help prevent derailments at the top or bottom of the grade.
A final consideration is to remember not to put turnouts immediately at the top or bottom of a grade. This also increases risk of derailments. The turnouts should be laid on a flat and level surface whenever possible.
Clearance is also an important consideration as you plan your layout. This refers to the distance required for your train to clear other trains or objects as it moves along the tracks. This could refer to either vertical or horizontal clearance.
If your train has to go under a bridge, you need to make sure that the vertical height between the tops of the rails and the underside of the bridge is greater than whatever the vertical height is of the locomotives, loaded freight cars and container cars that have to go under the bridge.
Horizontal or Lateral Clearance
Likewise, if you have long passenger cars or auto carriers going around curves, you need to be sure that you don’t put a structure, a rock, a telephone pole or other trackline accessory too close to the inside of the curve. If you do, you will have derailments as that long car scrapes up against that object.
You also need to be sure your tunnel portals are wide enough and high enough for all your equipment to clear them. If you have an arched tunnel that the trains have to go under, make sure the vertical height of the sides of the tunnel is adequate to accommodate the upper corners of the freight or container cars.
Of course, it’s always best to think about these things in the planning stages rather than discovering the disappointment later of not being able to run your container cars or your passenger cars through certain areas of your layout.
A good reference about grades and clearances in more detail can be found on the NMRA website at http://www.nmra.org/beginner/clearance.html.
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