Abstract: A conveyor having a plurality of groups of rollers 12 arranged to be driven from a chain 26 or other driving element, a clutch mechanism 22 being engageable to connect the drive chain, and the rollers 12 of each group so that roller drive is engaged or interrupted simultaneously, the system being capable of being used as an accumulator conveyor wherein goods units 10 can be moved forward or stopped in succession at the delivery end of the conveyor, a preparation system being provided to prepare operation of clutch mechanism 22 for groups of rollers 12, in readiness for the arrival of a goods unit which, actuating a sensor 43, interrupts drive to a group of rollers 12 and prepares a preceding group of rollers 12 to have the drive thereto interrupted.