So, why are manhole covers round?

I’m not all about turning this blog into the same thing as Wikipedia — because you can find the basic answer to the question posed above by searching ‘manhole cover’ on there — but I do want to use it periodically to address broader questions that no one really thinks about until it’s right in front of ’em. I’ll go back to trying to contextualize news tomorrow. I wanted to try and figure out this question because (a) apparently Microsoft started asking it in interviews and still does, about 20 years later (I interviewed there last October and wasn’t asked it, but I definitely wouldn’t have been prepared) and (b) some of my friends in grad school indicated to me recently that they’ve gotten similar-type queries in recent interviews. Odd.

This is purportedly one of the 10 toughest interview questions; it was designed to figure out how one would address a question with more than one correct answer. Circular covers don’t need to be rotated to align with the manhole, round tubes are the strongest against the compression of the Earth around them, etc. Here’s more detail. Nashua, NH used to have triangular manhole covers, but somewhat sadly, they’re being phased out because they’re too small. Bermuda and parts of San Francisco also use triangular manhole covers, so theoretically they do exist — they’re just not common.

Sidebar to all this: there is an entire Flickr set about the most unique manhole covers.  They can also blend into steps. They can be NSFW. They can contain maps of the city. They can be trippy and look 3D. They can also dance:

Jeez — these things are far more interesting than I had originally thought when I started this post. Maybe the next time someone asks you about manhole covers in an interview, you should answer the base question and then display your love of learning by running down some of the other angles in this post. “You know, sir, manhole covers are actually quite an interesting sub-topic of Americana…” That probably wouldn’t get you very far (read: anywhere). You might need a lesson in compassion — from a manhole cover.

Ted Bauer

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