Railroad Facts and Figures
Copyright AA Krug

What is a Tough RR Grade?

You have to look at the whole train to get a real feel for how hard a grade is. A 2% grade puts the headend of a mile long train 105 feet higher than the rearend. To put that in perspective, a two story house is about 20 feet tall. So a mile of 2% grade means you have to lift the entire train as high as FIVE 2 story houses one on top of the other.
Most trains are considerably longer than a mile. Often reaching 7,000 to 9,000 feet in length. A 7500 ft long train on a 2% grade has the headend 160 feet higher than the rearend. Put another way, as the train moves a distance equal to its length it has raised itself 160 feet. THAT is a lot of lifting.

A 1% grade can stall a train

Many railfans think that it takes a 2% or 3% grade to be considered a tough grade. I disagree.
ANY grade that completely loads the available power is a tough grade. Even grades of 0.8% or 0.5%
For instance a 1% grade can easily stall a train if it has more tonnage than the locos can pull up it. So if the 1% grade is the steepest grade on that section of railroad then the railroad is only going to put just enough power on their trains to barely make it over that hill. And that makes the 1% grade a very tough hill to pull. Every bit as tough as a 2 or 3% with relative tonnage and power.

A 1% grade can Break Couplers

In fact a 1% grade can be just as hard on equipment, breaking trains in two etc. Drawbars and knuckles are good for about 400,000 lbs of pull. If you pull much above that they will break. The normal figure used for trains on grades is 20 lbs per ton per percent of grade. So if we divide that 400,000 lb strength of the couplers by 20 lbs per ton per percent grade we get 20,000 tons for a 1% grade. That means the most you can pull up a 1% grade without breaking the couplers is 20,000 tons. And that is just the grade resistance not including the rolling resistance. Steep grades usually have many sharp curves and curves add to the rolling resistance. So the actual tonnage that can be handled up a 1% grade with only headend power is a bit less than this 20,000 ton value.
What about steeper grades?
For a 2% grade the maximum tonnage is about 10,000 tons and for a 3% grade would be about 7000 tons and a 4% grade would be about 5000 tons. Note that for each of these grades, 1-4%, the pull on the drawbars is EXACTLY the same! You are at the limit of coupler strength on any of them. Additionally, a loco in #8 throttle at 10 mph doesn't "know" if it has 20,000 tons trailing it on a 1% grade or 5,000 tons trailing it on a 4% grade. It is the SAME THING to the locomotives. They are working just as hard under any of these conditions as another.

Going Down

The main operational difference between grades of 1% or 2% or 3% is coming DOWN the hill. Now you have a big difference in the way a train handles with airbraking. The steeper grades are much more demanding and more dangerous. Each ton of train requires about 4 times the braking effort on a 4% downgrade as it does on a 1%. Because the available braking effort on each car is the same whether its on a 1% or a 4% grade descending a 2%+ grade is much more critical than lessor grades.
However,even this has a few caveats. Grades steeper than 2% usually have a speed restriction in the 15mph-25mph range going downhill. Whereas grades in the 1-1.5% range are usually traveled at track speeds of 50 to 60 mph or more. Much higher dynamic braking effort is generated at 15-25 mph than at 50-60 mph. Just try stopping an 18,000 ton coal train going 50mph down a 1.3% grade! I guarentee it will take as much airbraking and as much or more distance and time as a similar train going down a 2.5% at a much lower speed.

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Created 06-06-2001
Updated 06-06-2001