If they were friction less, they would be in balance without passengers and would start moving downwards with passengers stepping onto them at the top. And coul

If they were friction less, they would be in balance without passengers and would start moving downwards with passengers stepping onto them at the top. And could theoretically move a lighter group of passengers on another escalator upwards. In practice it seems very unlikely that one could make this work with reasonable effort. It already starts with the fact that you are probably not going to have well balanced streams of passengers in both directions most of the time.