When you are the only person on the train or on the train with only 1-2 other people from one end of the line to the other... yes that train is running empty that trip.  Similarly busses outside of the main rush frequently run with no more than 1-3 passengers.   That is how the average passenger count for RTD is 9 people a few very packed busses and trains and lots of nearly or completely empty busses or trains.