Track grade is the slope of a railroad track. The track grade is expressed as the percentage of its rise for the length of its run. For example, if you have 100 inches of model railroad track and the train climbs one inch, then the grade is 1%. So when 25 inches of track rises 1 inch, the grade is 4%. Maximum grade is the steepest slope your trains can climb. Well-planned grades can make a layout interesting. Badly planned ones can be a disaster.
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What's My Maximum Grade?
This is a common question on the online model railroad forums. The popular answer is, "Never use grades steeper than 2 percent." People seem to like simple answers even when the question isn't simple.
The largest manufacturer of model railroad landscape materials, Woodland Scenics, offers flexible incline foam for grading model railroad train layouts in grades of 2%, 3%, and 4%. If everyone followed the popular rule of thumb, it's safe to say that Woodland Scenics would not be selling 3% and 4% foam grade kits. As you can see from the diagram, these grades aren't very steep. But for real life trains, these are considered steep grades.
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Why Model Trains Can Handle Steeper Grades Than Real Trains
Some builders of prototypical model railroads will ridicule any grade steeper than 2%, perhaps not without justification. In real-life railroading, there are three classes of grades: 0.8% to 1% is "light grade," 1% to 1.8% is "heavy grade" and anything greater than 1.8% is "mountain grade." So perhaps it's not unreasonable to look askance at layouts with grades greater than 2% and call them "toy train" layouts. But that doesn't make it courteous... or kind. Maximum grade is frequently dictated by available layout space. The implied requirement is that if one is building a small layout it should be flat. But why not a mountain grade railroad over a flat oval or figure eight!
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Maximum Track Grade and Train Issues
So just what is the maximum grade you can use? Maximum grade is a function of three factors: the power of your locomotives, the weight of your locomotives, and the number and weight of the cars in your trains. That the locomotive's power is a factor is common sense; a weak locomotive won't pull many cars up a grade. But how the weight of the locomotive affects maximum grade isn't quite so obvious. The greater the weight, the greater the traction. This means wheels on lighter locomotives may slip where heavier locomotives can climb a grade. So larger scale locomotives may handle steep grades better than smaller scales. Good N scale locomotives can pull around 15 cars up a 4% grade. But to some modelers, 15 cars is too short a train.
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Grades, Like Curves, Are All About Space
With model train track curves our concern is the width of the space available to us. While curves can be used to break up the monotony of long straight sections of track, turning a train around with a180-degree curve, a necessity for continuous running layouts, taxes the limits of a narrow layout.
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.Continue to 5 of 11 below.
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Model Railroad Layout Overpass Clearances
The table at the left shows lists clearances in various scales for bridges and tunnels. Click the link so you can read it. The NMRA doesn't list standards for tunnel and bridge clearances that I have been able to find. Their vertical clearance standards are based on their "H" dimension.
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 didn't have sufficient clearance for models of modern locomotives and cars. And pantographs on electric locomotives increase clearance requirements too.
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Grading Runs for a Crossover
In order to raise a track to cross over itself, as in a simple figure eight, you need a grade that will raise the track to the clearance height. The table of clearances includes the lengths of the runs required to raise the track to the specified height for 2%, 3%, and 4% grades in various scales.
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 on the left shows N scale crossovers layouts for 2% and 4% grades. Ascending tracks are in green and descending tracks are in red. The 2% grade layout requires over 6 yards of length for the layout. Click on the link to enlarge the image.
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Split Your Track Grades
You can't shorten the total track grade length required for an over/under, but you can split your grades in half. To do this you raise the base elevation by one-half the tunnel clearance height. Then you use grades to lower your track for the under and raise it for the over. This technique requires four half-length track grades instead of two full-length track grades. It can also make your layout more interesting to look at.
The diagram at left shows our N scale figure eights with the grades split. The 4% grade layout now has a length of 3 yards. The blue outer curves are the midpoints of the grades. We could further shorten the layout by making the curves part of the grade. However, curved grades have additional considerations.
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Curved Track Grades
When you curve a grade, you increase the effective slope of the grade. The tighter the curve, the steeper your effective grade.
We made an 11-inch radius curve with a 4% grade in N scale. Our Athearn consolidation class locomotive would pull 9 of its Overton passenger cars over this curved grade with no difficulty. Then we made an 8.5-inch radius curve with a 4% grade. The consolidation would only pull 5 of its cars over this tighter turning grade. This grade was 1 inch high, half the N scale over/under height.Continue to 9 of 11 below.
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Multiple Unit Locomotives
When pulling longer trains, particularly in N scale, it is common practice to use the prototypical practice of pulling the train with multiple locomotives. This will also increase the size of a train that can be pulled up a grade, or the maximum grade for fewer cars.
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.
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Ghost Cars (Motorized Box Cars)
Another technique is to use a ghost car or "cheater car." This is a freight car, usually a boxcar, that is motorized like your locomotives. Ghost cars are usually put in the middle of a long train or spaced evenly throughout a long train if more than one is being used. Randgust makes a ghost car kit and Reality Reduced has a video on how to put it together.
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Top Tips for Managing Grade
What you need to know about grades can be summarized in two statements:
Always build your layout on layers of foam with the most track at the midpoint of crossover elevation. Then you can always split your grades going down for the under the track and up for the over the track.
When building a layout, before you glue down your grade foam and track always test your trains on the layout. Make sure your locomotives can navigate all your turns and grades, pulling whatever number of cars will be sufficient to ensure you enjoy the layout. If your favorite trains can't run on the layout, rethink your design. There's always a solution, but sometimes it takes a while to find it.
And remember, the most important point is to have fun!