Patrick Boylan wrote:...If they swap jobs, each crew member has less to walk to get between motorman and conductor postitions, and the conductor can get a 1 car head start, even further if they're willing to pass between cars while the train's moving...
You can't just simply walk through cars while the train is in motion! Those 3 car shuttle trains are packed to the brim with people (especially at rush hour), it would take you the entire trip to nudge your way through half a cars worth of people! Plus they keep lots of doors between cars locked nowadays to keep people from unlawfully passing between cars while the train is in motion, so the conductor will have to unlock, pass through, and re-lock 2 doors to go from one car to another.
But anyway, as others may have said, there is no conductor, the operators change jobs at each terminal. Under normal circumstances, nobody will leave their cab their entire shift. You see the same 3 1/2 blocks there, and then the same exact 3 1/2 blocks in reverse over and over again.
Here is an animated GIF I whipped up in MSpaint.exe that shows how the whole operator thing works (sorry if it's too small):