How are the doors on opposite sides of a subway train prevented from opening?

Question

I was on a NYC subway train, and I was thinking about how there are doors on both sides of the car. That got me thinking: how does the conductor or the train driver prevent the doors on one side of the train from opening when there is no platform on that side? If people are leaning against the doors and the doors open accidentally, that's a big problem. Is there any check system to ensure those doors don't open? Was there ever a time when the doors did open and someone fell out?

Just out of curiosity, you know...

Answer 1

different switches for each side, controlled by the conductor

Answer 2

cant help with this one ,however on the london underground they have a system that does prevent the doors from opening not only on the wrong side,but also out of the platform area