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The manhole cover thing was always confusing for me, as where I'm from manholes are all square.

Wonder if people where you're from run into problems where the manhole covers tip onto their diagonal and fall in (since that's the answer I memorized and I think is known as the predominant reason.)

Isn't actual reason that round shapes handle pressure better. So in the end it is about shape of the hole not the cover. As holes in ground are not square.

Then again I think here we have both, square and round. Square ones are more for rain runoff on sides of roads. Where as anything in middle of road are round usually with no grating and some rain water run off locations are also round for access again.

yeah I also memorized that answer, but my follow up question is: storm drain grates[0] seem to be commonly made in a rectangular form, why doesn't the same issue apply there?

[0] https://en.wikipedia.org/wiki/Storm_drain

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