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Model Train Track Grades and Maximum Grade Issues

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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 rise 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.

What's My Maximum Grade?

A common question on the online model railroad forums is, "What's the maximum grade I can use?" The popular answer is "Never use grades steeper than two 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, I think 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.

Track Grades: Prototypical vs. Toy Train

Some builders of prototypical model railroads will ridicule any grade steeper than 2%. And 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. I personally resent the implied requirement that if one is building a small layout it should be flat. I'll take a mountain grade railroad over a flat oval or figure eight any day!

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's 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.

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 a 180 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.

Model Railroad Layout Overpass Clearances

Table by author (Click to enlarge).
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, I've read of 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.

Grading Runs for a Crossover

Layout diagrams by author.
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 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.

Split Your Track Grades

Layout diagrams by author.
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 the our N scale figure eights with the grades split. The 4% grade layout now has a length under 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. But curved grades have additional considerations.

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. I'm not a physicist or a mathematician, so I can't give you exact numbers and equations to back them up. What I can tell you is that I know the physicists are right when they tell us this because I've proved it to myself.

I made an 11 inch radius curve with a 4% grade in N scale. My Athearn consolidation class locomotive would pull 9 of its Overton passenger cars over this curved grade with no difficulty. Then I 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.

Multiple Unit Locomotive Consists

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, I have seen modelers put locomotives in the middle of a train.

Ghost 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. I haven't seen ready to run ghost cars in local hobby shops, but Randgust makes a ghost car kit and Reality Reduced has a video on how to put it together.

Conclusions

What I have learned about grades can be summarized in two statements:

Always build your layout on layers of foam with most track at the midpoint of crossover elevation. Then you can always split your grades going down for the under track and up for the over 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 point is to have fun.
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