Anybody else notice they seem to be void of snow ie they stay clear of settled snow on roads and pavements. How come? Presumably made so they can be located and lifted in an emergency…?

simple the contents that flow through them are warm enough to melt the snow……..

Warm bathwater innit?

Manholes cover a few things. Sewers. Cable ducts. Stuff like that. All of which are likely to have a reasonably nice warm void below them, hence heating the metal lid. A lid that was permanently thawing the snow above it through any other means would be quite the miracle of thermodynamics, or be constantly powered electrically.

Of course cos hot air rises… I would have never thought of that honest! Cheers