Why Railroad Tracks Need Rocks

Added: 2026-05-25

[00:00:00]What if all the rocks underneath railroad tracks suddenly disappeared?

[00:00:03][music] At first, that doesn't sound like a big deal, but the truth is, without those [music] rocks, an entire train could derail. Years ago, railroad tracks were built with tiny [music] gaps between the rails. Because steel expands in the heat and contracts in the cold, whenever a train passed over those gaps, you'd hear the classic clickety-clack, [music] clickety-clack. But there was a problem.

[00:00:24]Those gaps limited how fast trains could go. So today, most modern railways use [music] long welded steel rails instead.

[00:00:31]One continuous track. That old clickety-clack sound has [music] almost disappeared. But now, when the steel expands in extreme heat, it has nowhere to go, and [music] that creates a dangerous amount of pressure. As temperatures rise, stress inside the rails keeps building, [music] and if that pressure isn't controlled, the entire track can suddenly bend and warp.

[00:00:50]For a high-speed train, that can become a deadly [music] disaster. And that's where these sharp rocks come in. They're called ballast.

[00:00:58]>> [music] >> Railroad tracks are attached to concrete or wooden sleepers, and those sleepers are tightly packed into the ballast underneath. The jagged shape of the rocks locks them together. [music] That creates massive friction. So when expanding steel pushes against [music] the track, the ballast holds everything firmly in place. Without these rocks, modern railways would be far more dangerous than most people realize.