Why Railway Tracks Have Gaps: The Man Who Cut Every One

Full animated episode, 4:07. Published 2026-11-11.

Why do railway tracks have gaps? Because steel grows in the heat, and a track with no room to grow can bend sideways on a hot day.

The story is made up. The science is real.

Chapters

0:00 Why railway tracks have gaps

0:14 Why the gaps change with the temperature

0:57 Why train tracks go clack clack

1:32 Thermal expansion: railroad tracks grow in the heat

2:11 Sun kinks: why train tracks buckle

3:13 Continuous welded rail: why modern tracks hide the gap

Sources

Steel grows in heat (about 12 µm per m per °C; a 39 ft rail grows about 5.5 mm with a 40 °C swing):

- Rail Engineer: https://www.railengineer.co.uk/?p=46262

- OpenStax College Physics: https://collegephysicsanswers.com/openstax-solutions/how-large-expansion-gap-should-be-left-between-steel-railroad-rails-if-they-0

Why rails were 39 ft (to fit 40 ft gondola cars):

Transcript

He cut a gap between every rail. You're building a broken railroad! First crew done gets every train in the state. Here's why he did it, from the first cut to the hottest day of the year. The other crew thinks he's lost his mind. Why not just push them tight? But he does something even stranger.

Every morning, before he cuts, he checks a little thermometer. On cold mornings, he cuts the gaps wide. On warm afternoons, thin. Nobody knows why, and he won't say. Then the new rails roll in, stacked in an open freight car. Thirty-nine feet? Make them forty and close the gaps! But a rail has to fit inside the forty-foot car that carries it.

So the rails stay short. And the gaps stay too. The other crew lays every rail end to end, tight as a zipper. One perfect line. And they finish first. Every train in the state! Their trains glide across the desert without a sound. His go clack, clack, clack. That sound is every wheel hopping over every gap.

The papers call it the Rattle Line. And the passengers switch to the quiet train. You cost us everything! He just checks his thermometer again. Then summer hits. His gaps start shrinking. In June, a finger fits. By August, barely a coin. Because steel grows when it gets hot. On his line, every rail has a little room to grow into.

But on the perfect line, there's no room at all. At night, its rails start to creak. That's just the desert cooling off. You know it isn't. If you like stories where the weird guy turns out right, subscribe, because the hottest day is next. The hottest day of the year. The thermometer on his belt is almost full.

And all along his line, the gaps finally close. Every gap, at the very same moment. Rail touching rail, and not one bit more. Across the valley, the perfect railroad has nowhere left to grow. So it goes sideways. The track bends like a snake in the sand. Railroaders call that a sun kink. And just then, the evening train comes around the corner.

Brake! Brake! Its wheels hit the bend, jump the rail, and the engine slides to a stop in the sand. The crew climbs out, dusty but fine, and stares at a track shaped like an S. Not one train runs on the perfect line that night. And the next morning, every train in the state goes clack, clack, clack.

So why don't trains clack like that anymore? Most of today's track is welded into one long piece, with no gaps at all. So where does the growing go? Remember his thermometer? Wide gaps on cold mornings, thin ones on warm days, so every gap would close on the very same day. Modern crews still check the rail's temperature.

Before they clamp it down, they heat it or stretch it, so it's laid as long as a hot day would make it. His gaps were made of air. Theirs are hidden inside the steel. But you can't stretch a bridge. So next time you drive over a big one, look down. Why is there a steel comb across the road?

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