Making Tracks

I don't speak "Railroad", so I don't know what the equipment is called that they drive up and down the tracks to rehabilitate old tracks that haven't been used in a long time. I try to imagine how they work, how they fix the tracks by driving up and down them. On my way to work, through the window...ugh...I saw 3 or 4 little track vehicles with people inside driving them. Much different than men with picks and shovels, like we used to see. Maybe this is an entirely different process. Sometime, I should do a little research and figure out what they're actually doing, but not tonight. Anyone know?