Abstract: A loader system for agricultural trailer boxes wherein a self-propelled carriage is provided with wheels to be driven on beams placed atop trailer boxes. The carriage supports conveyors extending over lateral sides of the trailer and the conveyors feed a chute emptying into the trailer interior. The beams of each trailer box can be linearly connected so that the carriage may be driven for one trailer to a queued trailer over a bridge formed by joining beams.