Steam rising out of manholes is definitely commonplace in NYC: [1]
There's a stretch of sidewalk in the Financial District that gets so hot that you can feel it walking past on some days. And apparently, sometimes these things explode... [2]
As far as I've heard it's not (all) actual leaks, though, but rather water dripping on the exterior of the hot pipes carrying the steam itself being evaporated.
It's often not the steam pipes leaking. The sewers are very humid and warmer than the air above. As the air convects up it hits the cold air and the humidity condenses. The same thing happens in lots of other cities when the weather is right.
Maybe the steam pipes keeps the sewers warmer in places with steam but they should be well insulated in the end.
you can see it pretty often in NYC, coming up from vents/pipes in the road
i don't think it's steam leaking. it's drainage/sewer water being heated by the steam system (and other heat sources down there) enough that it evaporates and rises up to the street, and then condenses into vapor/fog because the street level is cooler
