The one in the article is N Scale, but can be easily modified for other scales.
Ken Camozzi shows how he made a track cleaner using a boxcar and a piece of Masonite/Hardboard. (Also a link to an HO model.)
http://www.kencamozzi.com/
upnick
Good how to Poliss ... the Y3 in the video need the CV for the whistle /horn changing though to a deeper tone for such a sizable loco
poliss
One for HO/OO scale.
A Low Cost Track Cleaning Car You Can Build.