I was in Munich this weekend and noticed that almost all the escalators in the subway stations were bi-directional. When no one is there, the escalator is not moving. When it detects motion at the bottom of the escalator, it begins moving up. If it detects motion at the top, it begins moving down. The lighted symbols in the photos above indicate whether the escalator is running in your direction or the opposite.
Seems a bit banal, but this is a great energy efficiency idea. First, there is no point in having escalators moving with no one riding them. And second, making them bi-directional means you only need one escalator, not two.