In the municipal road, the reason of use of circular manhole cover, because the circular manhole cover is not easy to tilt,
can better protect the safety of pedestrians and vehicles.
The use of circular manhole covers is mainly on account of the length of each diameter of circular covers through
its center is same, so if the covers were rolled up by passing vehicles,
no matter how it rolling, its diameter forever is longer than the well,
manhole cover will not fall in the well.
