Education

Railroad tracks run all across America. It's nearly impossible to drive through a town, no matter how small, without coming across a set of railroad tracks. But have you ever looked down and wondered why every railroad track you see has the same rocks surrounding the tracks?

There's never a variation of colors, shapes, or sizes. You never see railroad tracks surrounded by pebbles or sitting atop the bare ground. If the tracks aren't encased in between metal and asphalt so cars can drive over them, they're surrounded by these rocks. Turns out, there's a very specific reason for this that even a quick Internet search may not explain without you having to peruse multiple sources.

Popping this question into a search engine will yield the result that the rocks are used for the expanding track, which is true. But there's so much more. These stones aren't just across America, they're under railroad tracks in any country that operates the fast-moving cargo and people haulers. The YouTube channel Simple Things - Surprising Histories shares some of the many reasons train tracks are surrounded by those grey rocks in one of their recent episodes.

Sunlit railway track stretching into the distance.Photo credit: Canva

"A loaded train is incredibly heavy. We're talking about millions of pounds of steel and cargo. If you place that much weight directly onto the ground, the intense pressure would crush the soil. The tracks would sink, buckle, and the eventual train would derail," the video explains before revealing that the stones are actually called "track ballast."

As the host moves along, they share that the entire thing is in layers, working together to allow the train to move smoothly along the tracks without sinking into the dirt. The very top layer is the metal track, followed by the horizontal beams, evenly spaced, called "sleepers." Those sleepers sit on top of the ballast, otherwise known as grey rocks, which act as a cushion for the weight of the train.

"It takes the immense concentrated weight of the train and spreads it out over a wide area. It dissipates the pressure so the ground underneath doesn't get crushed," they say. "But here is the fascinating part. The tracks are not fixed to the ground. If you look closely, you'll see the tracks are floating on the stones. They aren't bolted into the earth deep below. They rely on friction and the sheer weight of the ballast to stay in place. This flexibility allows the track to slightly absorb the vibration of a roaring train rather than snapping under the tension."

The type of rocks used to make ballast is also important to keep the train running smoothly. Jagged, rough rocks won't slide away from each other from the vibration of a moving train like smooth rocks would. According to Strasburg Railroad, ballast stones are a combination of crushed stones, rocks, and gravel used to prevent vegetation from sprouting and drain water from the tracks. The type of stones that traditionally make up a ballast are limestone, granite, basalt, and quartzite, which help disperse the high heat generated by a heavy, fast-moving train.

Who knew those stones were doing so much heavy lifting? Holding down the railroad track, absorbing the heat created, keeping weeds from growing, and allowing the track to expand to keep the train from sinking into the ground. Viewers were fascinated.

Train traversing lush greenery.Photo credit: Canva

"I had no idea that the tracks aren’t actually bolted into the ground. Amazingly interesting," one person says.

"I had no clue why I clicked on this video, but glad I did!!! Great info about something I never even considered. Thank you for sharing!!!" writes another.

"Grew up with tracks in my backyard. I grew up throwing these ballast stones. I could bullseye a target at a good distance. Never once considered their importance. Thanks!!" someone else chimes in.