Carriers/Trolleys Oftentimes a carrier is referred to as a trolley and a trolley is referred to as a carrier. Both terms are used interchangeably throughout the industry. Some prefer one name over the other but they are in fact, one in the same. To lessen the confusion we will refer to both as carrier/trolley throughout this website. A Carrier/trolley is a unit that travels along the bottom flange of a bridge girder or monorail track to transport a load. It is an assembly with 4, 8 or 16 wheels and is used to hold a hoist, a balancer, a manipulator and other types of equipment. Typically, two or more, two-wheeled heads are connected to a load block to make up a carrier. There are two types, hand propelled (hand-pushed) and motor driven.