In principal Bart[0] is supposed to be operated almost automatically and the train operator is there for announcements, closing doors and watching the track for hazards. In practice, the operator does a lot of speeding up/down manually. I can't find it now, but I remember reading an article that claimed that Bart trains were operated in manual mode 90% of the time, not sure the reason.

[0] https://en.wikipedia.org/wiki/Bay_Area_Rapid_Transit#Automat...