Hoisting and lifting construction materials is another of the most common functions of operating engineers.  Manipulating the controls of cranes, booms, and hoists, operating engineers service other crafts by lifting materials, supplies, and workers themselves from one place to another.  Tower crane operators are the single most important workers in the erection of a high-rise building.  Crane operators also lower materials into the deep tunnel projects that have been going on in and around the Chicago area for decades.