Can anyone tell me the science principle behind this effect. I was on a train in Kyushu, Japan and while the train was in motion, the glass separating the driver's cab from the passenger coach was transparent. When arriving at the station, he flicked a switch (presumably) and the glass became (almost) opaque. There was nothing mechanical like blinds or shutters involved and the glass stayed that way until starting off again. Although I've not seen it elsewhere, it may well be common- I'm just curious how they manage the effect.