They actually work pretty well and don't ice over for a couple of reasons. First, they are fed with geothermally heated water and don't use any salt, plus the roads in Japan are generally really nice and well drained, so no puddles to freeze to speak of. Second, they are only used for snow removal in areas where they get a lot of snow, but the temps don't get down terribly low. So, the water isn't ever exposed to cold that would freeze it before it drained away. It's all very Japanese.