What are the rocks on train tracks for?

The 'rocks' on rail tracks (well, between and around them) are called ballast. It serves several functions.

1) It prevents the rails from moving sideways which would be the natural tendency around most curves - the train would normally push the lines outward and the ballast stops this happening for the most part.

2) It provides a cushion and a bed for the track to lie on - the cushioning effect gives a smoother train ride and prevents hard jolting, and the bed means the rails won't sink into the ground in some places which would give a rollercoaster-like ride and be very uncomfortable as well as dangerous.

3) It aids drainage of the rail lines - the water will not be able to sit around the sleepers or ties which could rust or rot them, and similarly the steel rails, but it drains through the ballast and away.

4) It is an easy way to make a level running surface for trains - special track tamping machines are used to re-pack these ballast rocks around and underneath rails where they have been pushed out by the constant passing and vibration of trains. Much easier than trying to make a completely level track bed on the earth, and cheaper than using concrete beds all the way too.

Ballast is set between the tracks and sleepers to allow drainage of water. If dirt was placed there, water would not be able to drain, thus, rotting the sleepers and they would have to be replaced more often.

the rocks help the water drain away from the ties, so the ties last longer.

most rail roads run along waterways and they put the rocks there so hikers will have something to throw into the water.

It's called ballast, and yeah, maybe it might help prevent the tracks from sinking as previously mentioned. Most important, ballast provides stability on heavy traffic railroads. I've seen mining and logging lines that didn't use it. Ballast also serves as a porous medium that allows water to drain through, prolonging the life of the ties. In cold climates, the ground freezes and heaves in the winter just as lake ice will. The ballast allows the frozen ground to move beneath and reduce the effects on track alignment.

The stones are known as BALAASTS. It is used because, when trains pass at high speed there is a fear of tracks vibration. These balaasts absorb such shocks.

It's called ballast and is the foundation for the tracks. Just as the tarmac or concrete for a road is not laid straight on to the ground, neither are the rails of a railway. The ballast provides support and drainage and a level surface.

Incidentally, this question has been asked many times on this board and answers given,

They are to elevate and provide stability for the ties. The ties support the rails. Without this bedding, the ties would sink and it would warp the rails and the trains would derail.

To prevent the logs and rails from sinking into the ground.

Besides being a ballast for the rails, it also comes in handy if you happen to be walking on the tracks and need something to throw at somebody or something.......