"Darren New" <dne### [at] sanrrcom> wrote
> Warp wrote:

> >   You left out the fact that a round cover will not fall into the
manhole
> > no matter how you might screw up opening it.

> And what everyone so far has missed is that roads get repaved. The
> manhole screws into the vault at the bottom (so you can make it flush
> with the surface of the road) and has threads on the outside. When you
> repave the road, the first thing you do is give all the manholes an
> extra crank or two to lift them up an inch or so, so they stay flush
> with the surface of the road after you add more asphalt.

Another incidental benefit, but not the ultimate reason. Manholes have
always been predominantly round, even in cobblestone streets, which are not
designed for repaving higher, and where round bezels are actually often a
*liability* (See
http://images.google.ca/images?hl=en&q=cobblestone%20manhole ). Plus not all
manhole bezels are threaded in.

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