Different man holes for different utilities. Water, sanitary sewer, drainage, telephone long distance, telephone local, fiber optic.

Each utility owns there own lines and doesnt want to share. Cant have another company opening up and accidentally damaging a line.

Coordinating road construction is a nightmare

Is there ownership?

If one is marked Water/Sewer, and I am hired bu the City to work on stop lights, can I use that manhole?

People have grown in size over the last 100 years. Are all manholes the same size?

Not to mention, some of those utilities are laid down before roads are laid, and some of them were laid long ago way before the road systems in certain cities, limiting where you can really put access points.

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Slowguy

(insert pithy phrase here...)

Brain puzzle of the day:

Why are man hole covers round?

[scroll down for answer]








































Any other shape could fall into the holes.

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"100% of the people who confuse correlation and causation end up dying."

As a general rule we avoid mixing electrical utilities and water utilities. Single manholes 99% of the time only have a single utility, but a single fiber service may have a dozen actual customers. A water line manhole may be the convergence of 4 lines

The the actual structure below ground varies in size depending on the size of the line it is accessing and how deep.

Also so that the engineers/man-hole-cover-guys don't have to lift them to move it around - just roll it.

Not the only shape that wouldn't fall through. Another example is https://en.m.wikipedia.org/wiki/Reuleaux_triangle. Still a circle has that nice property and is probably easier to manufacture.

Ohh, man holes. I was way off when I opened this thread.

Cool shape!

And yah, "any other shape" was too strong in my first post.

That Reuleaux shape won't fall *all the way* through, but it looks like it could get wedged in the hole. (Is that pedantically falling "partially" through?) ;-)

FWIW, a circle won't get stuck, won't fall through, and doesn't need to be oriented to be put back. :-)

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"100% of the people who confuse correlation and causation end up dying."

Yea, saying they are circles because it is a shape that won't fall through is not really correct. It is more correct to say they are the most efficient shape that won't fall in. Because a circle would fall through the hole, but the circle is larger than the hole and rests on a ridge. So even a circle needs to be larger than the hole itself. For a given hole size, you could also make them a square, but that square would need each edge to the same as the diameter of the equivalent circle man hole cover. This would be a much heavier cover, making it hard to move, and also using more material, so more expensive. Also circles have the advantage of being able to be installed in any orientation, so much easier for a person to put back in place.

Yeah, yeah, yeah... ;-)

I knew my post was gonna get me in trouble with this group of pedants. But saying "a circle is the most practical, easily manufacturable shape that won't fall into the hole without undo excess material" isn't quite as snappy.

Then there is the "self-orienting" property...

:-)

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"100% of the people who confuse correlation and causation end up dying."

Now you have me looking out for manhole covers . . . Ran an errand and counted 10 covers on the drive. Only 4 in the path of wheel tracks, other 6 in the middle of the lane or not in the way. Maybe you just notice the ones you drive into?

Also, I would think the cover placement is so that it's directly over whatever they need to get to below. Unnecessary complication to angle the shaft, otherwise they could put it completely away from the road.

So interesting enough (ok, not interesting, maybe coincidentally) they were doing some work in the man hole in front of my house last week. Now whenever someone drives over it it’s noisy. Like it’s not sitting flush or something. Use to be perfectly quiet. Kind of annoying. But not sure I want to be that guy and call the city to complain about it.

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Matt

Yeah, I’m a bit disappointed myself.

Reminded me to clear my browser history though...

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Civilize the mind, but make savage the body.

- Chinese proverb

This guy wished he had looked out for manhole covers

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Brian

Gonna buy a fast car, put on my lead boots, take a long, long drive
I may end up spending all my money, but I'll still be alive

Man holes? You bloody chauvinist. Why do you hate women? They are called person holes here in Canada. All inclusiveness, you know...

Yikes. ... then the crane truck and the bridge! How is that allowed to happen ?!?

Typically corridors are set aside in the verge for utilities, ideally each with their default offset from property boundaries. This is at least the modern way but as has been pointed out by SG often the services were installed well before the road (and before such issues really came to light).

Nobody really wants the covers to be in the roadway. Not the asset owner* (difficulty in maintenance, worker safety/cars etc), not the road authority (complaints from motorists regarding traffic management delays, people driving across uneven covers, asset failures requiring the road the be ripped up), not the road user (obviously) and often not the adjacent landowner (covers can make a lot of noise). But there are a lot of competing services in the ground that often don't provide the ideal scenario. Manholes are typically placed at max centre/centre spacing for safety (working in confined spaces for larger assets like stormwater/sewer) and changes in direction, both vertically and horizontally (for stormwater in particular).

Rare that the same asset has more than one manhole right next to another. Where this can occur is where a road has been widened and a stormwater inlet (which has the trunk line connected) is no longer on the kerb so they install another inlet that connects back into the original one (now converted to a manhole cover).

When roads are resealed over time the contractor may not make the effort to raise the lid to the new finished surface, creating the annoying (and at times hazardous to bikes) depression.

It's expensive to relay long lengths of asset, so generally they tolerate leaving it running down the guts of a road

*One possible exception could be that the middle of the road is further from invasive root systems and less likely to be struck by an inattentive contractor digging around in the verge.

They've been holding motor races there since 2016. In that first year, Valtteri Bottas lost the bottom of his Williams for the same reason, has happened to a couple others as well. Maybe it's their defining feature? Paris-Roubaix : cobbles, Azerbaijan GP : loose manhole covers.

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Brian

Gonna buy a fast car, put on my lead boots, take a long, long drive
I may end up spending all my money, but I'll still be alive

I was asked that question once on an employment test and was told the answer is "so it can rolled (like a hula-hoop) instead carried".

If your answer is correct, why would they make drainage grates square?

Regarding rolling, I think that the "self-orienting" and "not getting stuck/falling in" properties are primary. (Though they're admittedly really heavy, how far are covers really ever rolled or carried?)

As to drainage grates, a square or rectangle has a bigger surface area than a circle for the same width, allowing greater flow through the drain, especially when they're off to the side up against a curb where a circle of the same flow would have to stick out farther into the road.

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"100% of the people who confuse correlation and causation end up dying."

Plus, who would want something that heavy with three points on it.

My first thought was this is about a bar in Chicago and this is the wrong forum for that discussion