Belt conveyors are used to transfer concrete horizontally and limited distances vertically. Conveyors made expressly for handling concrete are relatively inexpensive and may eliminate the need for other more expensive auxiliary equipment such as cranes. They are particularly useful in areas such as tunnels where space is limited and are widely used on building construction, especially large floor slabs and bridge decks. In massive construction, such as mat foundations, dams and power plants which require large quantities of concrete, conveyors are advantageous because of their placing capacities. Economy can be achieved through use of belt conveyor systems because the operating crew can be small in relation to the high rate of transport that is possible. For a series of feeder-type conveyors operated in tandem and set up to handle 200 cubic yards or more, the total labor crew would be eight to eleven men. This includes one man at the receiving hopper, two to four men handling the conveyors, two vibrator men and three to four shovel men. Conveyor units require just one more man than if the concrete were placed directly from the chute of the ready mix truck. A growing number of special types of belt conveyors are available. Several manufactures produce conveyors that are mounted on trailer-like frames with wheels for easy movement around the job site and between jobs. Belt conveyors mounted in tandem on the extendable boom of hydraulic cranes are also available. These units have a complete 360 degree swing and some models can reach out as much as 135 feet and discharge concrete at a height of 80 feet. Also, telescoping conveyors are available mounted on conventional over the road trucks. As with the crane mounted units, they can swing, reach and retract while the belt discharges concrete into forms located at grade, above grade, or below grade. Other special types of concrete conveyors are known as side discharge and radial spreader units.