Ever wondered why there are crushed stones lying between and outside of both the sides of a railway track. Here is the reason.
What we call sharp edged stones are dubbed ‘ballast’ in railway jargon. When we board a train and experience a smooth journey without accidents, this is because of these ballasts.
Before laying down a railway line, a track bed is prepared. To prepare this, first two layers of soil are laid out. Then a layer of crushed stones is spread over the soil. Thereafter, pre-stressed concrete plates are placed with equal gap between them. These rectangular sized plates are called sleepers. Earlier, they used to be wooden ones. Thus, the track bed is prepared. Upon its completion, railway tracks are laid out. The ballasts help in holding the sleepers tightly.
Now imagine what would happen if there were no ballasts between the tracks. In that case, when a train moves along the track, the sleepers get displaced, resulting in mishap.
From this, it can be understood why round shaped pebbles on riverbeds are not given a try.
The other advantage of using sharp edged stones along the tracks is that they help rainwater seep first and stop growth of vegetation which could otherwise loose the soil underneath.