[harrison_clarke]

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

[triceratops]

That's what I figured.