Thoughts from a reflective educator.
People go up escalators, people go down escalators.
What if the energy potential of the people going down an escalator was used to power an escalator going up? You'd still have to add energy to the system, but there should be some way to save at least some of the energy used when the escalator carries many thousands of kilograms of people down, to help power the escalator on the up side.
Clearly this type of system would work best when the relative rates of people going up and down on the escalators are approximately equal. In many rush hour situations, this simply isn't true. However, even a modest savings of energy for a system which runs 24/7 every day of the year would be worth exploring.
Update: It seems to me that this idea is not likely to be original, and that someone has probably implemented it. Let me know if this is the case, and I'll update this post.