If we had the technology to transport additional weight at no additional energy cost, the world would be very different. Elevators HAVE to use more energy when there are 400 lbs of people in them. The fact that Shabbos elevators are not assur must imply that those poskim were OK with that extra energy usage for whatever reason. I’ve never understood how walking through the motion sensor on the door is mutar on those. If they disengaged it, it would mean the elevator door could potentially crush someone to death on a Shabbos elevator, so I refuse to believe it’s inactive on Shabbos.
DY: Do any of your sources say that Shabbos elevators are mutar, but escalators are not? I’m curious, because it does seem like escalators would be less problematic.