weights of trucks and containers. This allows the tare weight to be looked up and eliminates the need for a second weighing. Roll-offs are placed by roll-off trucks. As the roll-off truck raises its hydraulically operated bed, the roll-off container rolls off the bed. A cable is used to slowly lower the container. After the waste container is loaded, the roll-off truck pulls the filled container onto the roll-off truck with the cable and winch system. If the roll-off truck is not a winch system, then it is most likely a hook-lift system. A hook-lift system works by the truck extending a 90 degree arm with a hook on the end which hooks under a bar and gently lifts the dumpster onto the truck. Most hook-lift systems are on smaller roll-off trucks as they are usually used for 20 yard containers and under. These smaller systems are usually the preferred option on smaller scale construction jobs such as roof replacement, kitchen remodels, and garage clean-outs. Smaller single-axle trucks are generally viewed as safer operations as they are much lighter and more easily transported in residential areas. When carried the roll-off must be covered. Cost factors There are three parts to roll-off dumpster pricing: dump rate, haul rate, and overage fees. Dumpster rental companies pay the landfill, transfer station, recycling center, or other type of disposal facility a fee to dump the customer's waste. Fees fluctuate from area to area and facility to facility. Dump fees can be the majority of the cost for the dumpster, and are measured in short tons in the U.S. The haul rate is the rate that roll-off rental companies charge to cover operating costs and generate profit. Overage fees are additional fees the customer must pay if the dumpster is loaded more than the allotted tonnage limit. Overage fees are typically prorated and the same as the company's dump rate. Disadvantages One problem often encountered with roll-off containers is the liability of scratching or damaging the surface they are placed on. Most roll-off containers have metal rollers for wheels, which can at times scratch or be abrasive to a concrete or asphalt surface. It is recommended to place a protective board such as plywood under the container to avoid a situation where the placement surface can be damaged. Most roll-off companies do not offer plywood, but will place the container on the wood if supplied.