Probably because of all the history classes we all took in grades 1 through 12, many people have a impression of the railroads that comes from the 1800s. We imagine hundreds or thousands of men building railroad tracks using hand-carried wooden railroad ties and hammers. Something like this:
The following video has made the rounds since it was released, with well over half a million views. It is fascinating in a “How It’s Made” sense, because it shows an amazing amount of automation now used in the process:
The only problem is the lack of an explanation of what is going on. Each machine is accomplishing a specific task. At the beginning some of these tasks are pretty obvious, like the machines that fetch concrete ties and then lay them on the track. But what, for example, is this machine doing?
This is a tamping machine, designed to pack the ballast (gravel) around the ties, in this case made by Plasser & Theurer:
A ballast tamper or tamping machine is a machine used to pack (or tamp) the track ballast under railway tracks to make the tracks more durable. Prior to the introduction of mechanical tampers, this task was done by manual labour with the help of beaters. As well as being faster, more accurate, more efficient and less labour-intensive, tamping machines are essential for the use of concrete sleepers since they are too heavy (usually over 250 kg (551 lb) to be packed into the ballast by hand.
Early machines only lifted the track and packed the ballast. More modern machines, sometimes known as a tamper-liner or tamping and lining machine, also correct the alignment of the rails to make them parallel and level, in order to achieve a more comfortable ride for passengers and freight and to reduce the mechanical strain applied to the rails by passing trains.
What is the following machine doing?
It is a ballast cleaner. It removes all of the ballast, in this case to lay geogrid fabric underneath. But the main reason for pulling out the ballast like this is to clean it. As the track ages, the ballast gets crushed. The ballast cleaner runs the ballast through a screen to remove all the small pieces (and sand) and replace them with correctly sized ballast.
For more information on the track-laying process, this documentary can be helpful: