Many cranes have large overhanging booms that make up a significant portion of the machines overall weight. Boom dollies help support the weight of the boom to prevent cranes from being overweight on their own axles and are also useful for travel during road bans. The number of axles on a dolly varies based on the weight of the crane it is used with. They all feature a sliding boom platform that pivots to allow movement in corners and uneven terrain.