I was waiting for my train at the metro station and noticed that all the escalators continuously operate when there are barely anybody riding on them. Wouldn't it be a good idea to just dynamically start/stop them? With all the green talk these days, wouldn't this really save a lot of energy? I will admit that i don't have enough knowledge about escalators so i apologize if i sound ignorant.

From my basic research (googling, wiki, etc) seems like escalators require a power supply of 50 Hz to 60 Hz [source]. Saving a little by dynamically start/stopping an escalator might go a long way considering there are 30, 000 elevators in US [source]. Again i have to show my ignorance here because i don't exactly know what goes into instantaneously starting/stopping an escalator. Let's assume that is not a lot of overhead and discuss how they can be started/stopped. I think this is very easily possible using a simple infrared sensor. If the sensor detects somebody approaching it will gradually increase in speed so there is no sudden kick the minute a rider steps on. Multiple sensors can also be used just to be absolutely sure and redundancy.

There are a lot of assumptions and simple over looking of facts here but i really am curious about this. It just seems such a simple fix might actually help conserve a lot of energy worldwide or maybe not. Hopefully someone can enlightenment me on this.