"The Plasser American RM 802 is a High-Production Ballast Undercutting/Cleaning Machine especially designed to work on track with pre-dumped ballast.

The Ballast Pick-up Unit picks up the pre-dumped ballast and moves it onto conveyor belts. A transition conveyor belt fills the first of several MFS type Ballast Conveyor/Hopper Cars. With the help of these units, it is possible to bring new ballast to the worksite. The cutting chain excavates the ballast and passes it on to the screening unit. Here the reusable ballast is separated from waste material. A system of conveyors transport the waste material to the end of the machine, where it is discharged. The cleaned ballast is mixed with the pre-dumped, picked-up and stored ballast and put back to the track directly behind the cutter chain. When working in curves, the shaker boxes can be adjusted to compensate for superelevation. With the RM 802, production rates of up to 2,000 feet per hour are achievable."
http://www.plasseramerican.com/en/p_cleaning/rm802.htm