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Trees and Trains

Jonn Leffmann
Wiki Commons

I recently took the train from Salt Lake City to California, my first such experience in decades. Each mile, my train passed over 3,000 railroad ties – nearly all of them made from trees.

Railroad ties, or cross ties, are a critical ingredient of railway tracks. They transfer the tremendous weight of cars and cargo to the track ballast, the crushed gravel bed that underlies the rails and help maintain the right gauge, or distance between the tracks.

In the 1830s, the first railroads were secured onto stone blocks. But as locomotives became heavier, wooden railroad ties were introduced. Workers hand cut rough ties from trees with cross saws and broadaxes, jobs that were replaced by sawmills in the 1940s. Today, crossties have a uniform size and thickness, 10 inches thick and 10 feet long.

Nationwide, freight trains now move nearly two billion tons of goods across an astounding 450,000,000 railroad ties. Nearly all of them are made from wood — less than 2% are made of steel or concrete.

Ties from trees persist because wood is strong, flexible and renewable, and it doesn’t conduct electricity or interfere with electronic rail monitoring. But because wood is subject to decay, cross ties must be treated with liquid wood preservatives, like creosote, a type of coal tar. Treated crossties can last for more than 30 years.

If a rail company chooses ties made from one of our deciduous trees — like oak, maple or hickory — the liquid preservative can easily permeate throughout the wood because of the open-ended cells that transport water within deciduous trees.

If the company goes for wood made from conifer trees — like Douglas-fir or hemlock — they’ll be less expensive and lighter-weight, but will be less absorptive of preservative, since their transport cells have closed ends that allow for one-way transfer of liquids.

On my recent railroad voyage, I encountered members of the Railroad Tie Association, who are as enthusiastic about railroad ties as I am about trees. That organization was founded in 1919 to promote the sound use of wood crossties. Their annual meeting takes place each October. I think I might attend! And I'll take the train there, counting those wooden ties as I go.

Dr. Nalini Nadkarni is an emeritus professor of both The Evergreen State College and the University of Utah, one of the world’s leading ecologists and a popular science communicator. Dr. Nadkarni’s research and public engagement work is supported by the National Geographic Society and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. @nalininadkarni
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