What do the subway track lights mean?

Ever heard this one: “Because of a trouble, uptown/downtown _____ trains are running ______ ”

Ever wonder what the signal lights really mean?  It’s a little more complicated than a normal traffic light.  For example, when you really pay close attention, you might notice stacked sets of lights.  One might be green, and another might be yellow.  What the heck does that mean?

Well, I stumbled across a fabulous article on “How Stuff Works.”  Who knew?!  They have an article about how the subway works.  It covers more than just the lights and signals.  This is one of the many helpful illustrations they have.

So check it out.  Some pretty cool stuff I bet you didn’t know.