Why are There Gaps in Railroad Tracks?

Mary McMahon

When people think of trains, they often think of the distinctive clickety-clack sound caused by a train as it rolls along the rails. This sound is caused by tiny gaps which are built between sections of railroad track, as people who have inspected rail tracks closely may have noted. These gaps are deliberately placed to ensure that the tracks will not buckle in extremely hot weather when the tracks expand.

Welded tracks are used for high-speed trains.
Welded tracks are used for high-speed trains.

The distinctive gap in railroad tracks hasn't always been there. Initially, designers of railroads butted the tracks right up against each other for a smooth ride. However, they noticed that in the winter, tiny gaps would form between sections of track, and in the summer, tracks would deform and buckle, increasing the risk of derailment. This is because metal contracts in response to cold, and expands in response to heat.

Railroad tracks must be carefully inspected on a regular basis.
Railroad tracks must be carefully inspected on a regular basis.

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When rail companies realized the problem, they started including gaps in railroad tracks, which allowed the metal to expand in warm weather without buckling or tearing up sections of tracks. However, the gaps must also be designed to accommodate shrinkage in cold weather, because if the gap gets too large, it can cause navigational problems for the trains which pass over it, especially in the case of extremely heavy trains. Therefore, the size of the gap must be carefully chosen, taking the specific properties of the metal used into account.

Gaps in railroad tracks keep the tracks from buckling in hot weather.
Gaps in railroad tracks keep the tracks from buckling in hot weather.

These distinctive gaps are known as expansion joints. Depending on where they are built, the gaps in railroad tracks may be staggered, so that the train only pass over one gap at a time, or they may be evenly matched. Staggered expansion joints are most common in the United States. Because of the stress on the tracks at the site of an expansion joint, railroad tracks must be carefully inspected on a regular basis to ensure that the bolts joining sections of track are not coming loose.

Because the gaps in railroad tracks can cause problems and they are difficult to maintain, some railroads prefer to use welded tracks. These tracks must be specially welded so that the tracks do not grow weak at the site of the weld, as the metal will continue to expand and contract in response to the weather. Welded tracks are used for high-speed trains, where a smooth ride is of the essence, and they are growing increasingly common, thanks to the development of superior welding techniques.

Railroad track gaps are designed to allow for shrinkage in cold weather and expansion in hot weather.
Railroad track gaps are designed to allow for shrinkage in cold weather and expansion in hot weather.

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Discussion Comments


I have a question for anyone out there. I live near a railroad track that is long abandoned. I know it is an abandoned railroad track because there are dead cars on the track, segments rusted through, and the track is actually broken up in places. Is it legal for someone to go and tear up abandoned track and sell the metal for scrap? Who should I talk to about this?


@ Anon40521- This is also safer because sensors in the track detect breaks in the track from shrinkage. Track sensors, on the other hand, do not detect Sun kinks. If the track is laid when the rail is at its maximum temperature, it will not expand any more than it was when it was laid. This will prevent derailments from track becoming slack and kinked.


@ anon40521- When engineers join track to make welded rails they heat or stretch the track to the length they would stretch to under maximum temperature expansion. As long as long as engineers lay the rail down with enough lateral support, the rail will hold its shape to the ties. This keeps the track as taught as possible, and with adequate lateral support, the track will not shrink.

When welded tracks do come to a joint, engineers create a breather switch to allow for kink and shrinkage that could be damaging to the wheels and dangerous to the train. Engineers join the track at a diagonal rather than an angle perpendicular to the ties. When the track expands, one track slides over another accommodating the expansion. When they shrink, they slide away from each other, but they remain overlapped, causing only a tiny dip. Engineers join the breather switch with special plates that give very good lateral support.


Welded tracks are all very well but does not stop expansion in hot weather so how is this expansion dealt with so that the track does not buckle?

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