Why are Manhole Covers Round?

This question may seem very random, unnecessary, or you may think there is no real reason why manholes covers are round instead of trapezoidal, triangular, or shaped like a rhombus. But I found that the reason for a round manhole is very justifiable.

While doing research, I found that although it may not seem like it, creating a manhole cover a little bit of engineering to come up with the right measurements. One benefit of having a round cover for a manhole is it won’t and can’t fall into the hole. For example, look at a square. If you turn the square cover with a corner pointed down it could easily fall down into the hole. Same goes for ovals, triangles, and other similar shapes. Also, when cars are driving down the road, a square or other pointed shape is more likely to lift up and hit the cars tire when it is ran over. A circular cover stays in place. Circular manhole covers are also easier to roll and navigate along the street. The other advantage of having a circle cover is you do not have to line up the edges to make it fit. This may even save a few seconds which increases job productivity. As you can see, even a very trivial question such as this has answers. You just have to know how to navigate around the internet and get straight to your answer. http://www.straightdope.com/columns/read/220/why-are-manhole-covers-round