system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are there crushed stones alongside rail tracks ? what is there use and what will happen if they are not there ?
gpt
The crushed stones are called track ballast on which the sleepers (ties) are laid. The sleepers bear a lot of weight, the ballast helps them  bear the weight. They also allow water to drain through and also prevents creepers and weeds from growing on the ground beneath the tracks. They hold the ties in place which hold the tracks in place and distributes the weight of the train equally which would otherwise overwhelm the sleepers or the tracks and they would  sink into the ground.