A Union Pacific undercutter works on main 2 at McGrew, Nebraska, over the South Morrill Subdivision on July 26, 2009. UP No. 902053 is a Plasser & Theurer RM 2003 undercutter that specializes in cleaning ballast. Over time, ballast can break down, and other impurities like sand and dirt can further create drainage problems in the track structure. This machine excavates under the track to various depths, with a series of conveyers taking the “dirty” ballast through screens, sorting out the fines and contaminants from good ballast, and depositing the “cleaned” ballast back onto the track with a oscillating return conveyor and distribution plow. The waste materials are discharged using conveyors that deposit the material to either side of the right-of-way, or into open-top railcars. The RM 2003 has the ability to lift the track to reduce the cutting depth when required, and can even shift the track laterally to clear trackside obstacles when needed. In this view, two different conveyors are being used to deposit the fines sorted from the ballast to the south side of the main line.
