If you notice that your train slows down or stops only in some places the problem may be the result of voltage drop. The probable causes are that the distance from the nearest power source is too great or that the quality of the joints between track sections weaken the flow of power.
Tighten any loose joiners and if necessary, run a second set of wires from the power supply to the track in the troubled area. Make sure to connect each wire to the proper rail.
On large layouts, particularly with most DCC systems, it is recommended that a bus wire with feeders to multiple track sections is used. Also using a heavier wire is much more efficient than using the rails themselves. Smaller feeder wires between the rail and the bus, can be attached as often as necessary. Typically, feeders are attached every six to twelve feet.
In addition, you can also solder the rail joiners themselves. This will greatly reduce voltage drop and also help eliminate kinks that can cause derailments. It is a good idea to leave a few joiners open to allow for expansion and contraction throughout the year.