This train of four gondolas pulled by a heavy-duty road-rail truck came through this morning making a lot of clanking noises.
These pieces of equipment are equipped with magnets and are used to pick up tie plates and drop them alongside the tracks. A tie plate, in case you were wondering, is a metal plate that sits on the wooden ties (sleeper in British parlance). The rails sit on the plate, and the spikes that hold down the rail are driven through holes in the tie plate. This spreads the load better onto the ties and then down into the ballast.
This train makes a lot of racket while unloading all of that metal. I took some video to give an idea of how loud.
I assume that a train similar to this one will be through in a few days dropping bundles of ties, after which the crews that turn rails, ties, tie plates, ballast, and spikes into a railroad track will arrive.
This being a main line, it has to be relaid every few years. Typically the main line rails, if not obviously damaged, can be re-used for lighter-duty tracks. But if the rails are shot, they can of course be melted down and re-rolled, and lots of the metal pieces can similarly be recycled. Only railroad ties are a problem. They're toxic, being creosote-treated wood, and it takes specialty installations to dispose of them safely.