It was pouring rain and not exactly ideal for photography, but this scene
caught my attention as we were driving into Nanaimo. The first thing that
struck me when I saw the port switching yard at the harbour was the
maze of tracks, then I moved on to, 'how in the world does this thing work?'.
After we returned home I found the following explanation at wikipeidia.com:

Switching yards are used to separate isolated railroad cars on to one of
several tracks. The inbound trains are broken up and sorted into outgoing
trains according to their various destinations. This sorting is done partly
at the starting and final destinations and partly (for long-distance-hauling)
in classification yards.

Freight trains that consist of isolated cars must be made into trains and
divided according to their destinations. Thus the cars must be shunted several
times along their route in contrast to a unit train, which carries, for
example, automobiles from the plant to a port, or coal from a mine to the
power plant. First the cars are taken to a track, sometimes called a lead
or a drill. From there the cars are sent through a series of switches called
a ladder onto the classification tracks. Once the sorting is completed the
sorted cars are connected together, then they wait for pickup by the next
train or ship going their way.

To see postings of others participating in January's Monochromatic Challenge click HERE