I still don't understand why that takes a separate job. Most other subway lines the operator does this too, even barks on the PA and sounds an alarm over the problem door, as well as has an internal camera they can switch on to see inside the car, but you don't need a second staffer because by definition the operator is no longer driving while doing doors at the station. MTA on the other hand has decided it needs to pay at least one person to sit and do nothing at all times during the train operation: the train operator who does nothing while the door operator futzes at the station, and the door operator who does nothing while the train is traveling.