Now that the inventor has confirmed how he did it, I was inspired to experiment with this special-effect even though I don't run subways!
I don't have the short track sections he used so after initially trying to cut an outer rail with a hacksaw, I gave up and used a bandsaw to cut from the edge to make two outer-rail isolated islands - I figure some putty and gray paint could touch up the bed if need be. 3mm cool-white LEDs are installed from the bottom through 1/8" holes. With a diode attached to center-rail and 1 resistor per LED taking track power as previously diagrammed, here's a short video with a streetcar which is closest thing I have to a subway.