Trains are efficient; very efficient, the ultimate public transportation system. For instance, a freight train can move 2000 lbs of freight, 457 miles on only 1 gallon of fuel. This is like a 457 mpg car.
Trains are efficient for a number of reasons. One example is a low rolling resistance.
- A rubber tire on pavement has a resistance is 6 to 10 times greater than a steel wheel on a track. This is because the rubber tires deform under load. This is a severe efficiency loss, imagine towing something on a semi circle wheel (exaggeration). As seen below in comparison to a steel wheel.
- There rubber tires generate a significant amount of friction too. Feel how hot a tire is after a run.
- Tires have a significantly smaller radius than a steel wheel and are wider, contributing to more rolling resistance. “The coefficient of rolling resistance is proportional to the width of a wheel and inversely proportional to its radius.”
- Also, railroad axles can handle 80,000 lbs. This Reduces rolling resistance by placing more mass on the wheels (counter-intuitive but true).
Air resistance is one of the main causes of inefficiency. And much R&D must go into improving this.
See the train on the left vs train on the right. As the left train approaches air hits it and collects in front of the train. A “vacuum” is created temporarily on the back and air rushes in. As the train moves air rushes into the side to fill the void. This is quite chaotic and results in efficiency losses.
The train on the right resembles a double airplane wing and creates no pressure extremes or inefficiencies, optimal for high speeds.
Another factor is the spacing between cars vs train cars. The freight train cars have a very low distance in between them, decreasing air resistance. However, the distance between cars can be very high, resulting in inefficiency.
Now that we have cleared up some understandings, lets examine our goal.
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