They work in a black hole, beside live rails with trains bearing down just centimeters off the way.

This is the track simulation room. 46 meters of subway recreated down to the last wire, tie and boat.

The only difference, these rails are lifeless.

In the field, they carry a leaf or dose of electricity, 600 volts.

With crews working centimeters from death, accuracy counts.

Bob Guerinel is one of the instructors.

Students get the chance to take apart their equipment,

to adjust their equipment to get a true feel for what they are gonna experience when they are out in a real world,

doing the actual job and keeping New York City safe.

Workers keep the signal system running,

and the signal system keeps the trains running safely.

It works through modern electronics and old-fashioned mechanics.

All tracks are divided into 300- meter sections called blocks that electrically detect the presence of a train.