---
title: 'Why Don''t Trains Make That Sound Anymore?'
source: 'https://youtube.com/watch?v=MVFd0qFB9TE'
video_id: 'MVFd0qFB9TE'
date: 2026-08-27
duration_sec: 63
channel: 'Veritasium'
---

# Why Don't Trains Make That Sound Anymore?

> Source: [Why Don't Trains Make That Sound Anymore?](https://youtube.com/watch?v=MVFd0qFB9TE)

## Summary

This video explains why modern trains no longer produce the classic 'clickety-clack' sound, attributing it to the shift from gapped tracks to continuously welded rails. It details how jagged ballast rocks are used to manage thermal expansion and prevent track buckling.

### Key Points

- **Historical Track Gaps** [00:02] — Train tracks used to have gaps to allow for thermal expansion and contraction, which caused the rhythmic 'tuck-tuck' sound as wheels crossed them.
- **Shift to Welded Rails** [00:15] — Modern tracks are welded into seamless rails, eliminating the clickety-clack but creating a new problem: expanding rails have nowhere to go, risking violent buckling.
- **Role of Jagged Ballast** [00:29] — Tracks are attached to sleepers and embedded in jagged rocks that interlock, creating friction that holds the rail straight under thermal pressure.
- **Why Smooth Rocks Fail** [00:54] — If ballast rocks were smooth and round, train vibrations would cause them to slide, leading to rapid track buckling.

### Conclusion

The video concludes that the jagged ballast rocks are essential for maintaining track stability by counteracting thermal expansion, a clever engineering solution that also eliminated the iconic train sound.

## Transcript

train tracks used to have gaps in tracks expand and contract with temperature. And wheels hitting those gaps made that the tuck the tuck the tuck sound. But those gaps also slowed
the trains down. So, today's tracks are welded into one seamless rail. No more clickety-clack. But now with expanding hot rail has nowhere to go. And if left alone, the internal pressure would build until finally the rails would violently
buckle into the zigzag. And that is where those jagged [music] rocks come in. The tracks are attached to these sleepers and then embedded in those [music] rocks. And their jaggedness makes them physically interlock, which
creates a huge amount of friction. So, when the steel rails expand and [music] push on the sleepers, the jagged rocks lock together and hold everything firmly in place. That keeps the rail straight even under huge internal pressure. But
if the rocks were smooth and round, then vibrations from passing trains would make them slide around and the [music] track could quickly buckle. Subscribe track could quickly buckle. Subscribe for more.