A manhole is an opening to a confined space such as a shaft, utility vault, or large vessel. It is often used as an access point for an underground public utility, allowing inspection, maintenance, and system upgrades. Manholes are typically found in sewer systems, and they are used by utility personnel as a point of access to the system. They are designed with a cover or lid and comprised of grade adjusting rings, a top tapered section called the cone, a main cylinder section called the wall or barrel, and a bench and channel where the waste flows through. Manholes are usually round because roundness is the best shape to resist the compression of the earth, and covers are round because they are easier to manufacture than square or rectangular shapes, they are easier to move by rolling, and they cant fall into the opening. However, in the United Kingdom, they are nearly always square or rectangular in shape, at least at street level. Manholes can also be found in a triangular shape in some places. There are three different types of manholes: shallow, normal, and deep. "Normal" manholes are typically 4- to 5-feet deep and wide enough for the average person to fit in, while "shallow" manholes are 2- to 3-feet deep, often placed at the start of a sewer branch and in areas with low traffic. Manholes with a depth greater than 5-feet are considered "deep" and usually have an entry method like a ladder built-in, as well as a heavier cover. Manholes are mainly positioned 0.5m away from the curb lines of the road and constructed such that they are away from the wheel line of the traffic. The covers used for manholes can be either rectangular, square, or circular in shape, and the material of the cover can be precast concrete, composite material, or any glass-reinforced.