KEEP EXPLORING
First fix the cause
Repeated black residue may come from dirty wheels, airborne dust, scenery materials, lubricants or track-cleaning products that leave films. Cleaning rail without cleaning wheels can quickly transfer contamination back to the track.
Routine
Vacuum loose dust, wipe rail with a suitable non-abrasive method, clean locomotive pickup wheels, inspect feeders and exercise turnouts. Avoid excessive abrasive polishing that leaves rough surfaces which may collect dirt faster.
Hard-to-reach track
Hidden trackage should be built with access in mind. Track-cleaning cars can help, but they are not a substitute for the ability to reach problem areas.
Electrical reliability
If a section repeatedly loses power despite clean rail, investigate feeder connections, rail joiners, turnout contacts and bus connections rather than cleaning it again.