An apparatus for sorting a plurality of items, comprising: a plurality of sort destinations; a plurality of delivery vehicles for delivering items to the sort destinations, wherein each vehicle comprises: a surface (212, 605) for supporting items to be delivered; and an edge-detection assembly (500, 602, 604) for detecting an edge of an item when the item is conveyed onto or discharged from the vehicle, wherein the edge-detection assembly comprises: an emitter for emitting a beam of light toward the surface and configured to form a light curtain within a detection plane,; and a plurality of detectors for detecting the beam of light, wherein an object on the surface of the vehicle affects the beam of light received by the detectors; a controller for controlling the loading of an item onto one of the vehicles or the discharge of an item from the vehicle based on signals from the edge-detection assembly, characterized in that the plurality of detectors is a linear array of photodetector, and in that the emitter is positioned below the surface so that the beam of light is projected transverse to the surface, and the edge-detection assembly (500, 606) is positioned adjacent to, but slightly below, a discharge end of the surface so that the emitter and plurality of detectors form a detection plane that is transverse and orthogonal to a plane defined by the surface. a plurality of sort destinations; a plurality of delivery vehicles for delivering items to the sort destinations, wherein each vehicle comprises: a surface (212, 605) for supporting items to be delivered; and an edge-detection assembly (500, 602, 604) for detecting an edge of an item when the item is conveyed onto or discharged from the vehicle, wherein the edge-detection assembly comprises: an emitter for emitting a beam of light toward the surface and configured to form a light curtain within a detection plane,; and a plurality of detectors for detecting the beam of light, wherein an object on the surface of the vehicle affects the beam of light received by the detectors; a controller for controlling the loading of an item onto one of the vehicles or the discharge of an item from the vehicle based on signals from the edge-detection assembly, a surface (212, 605) for supporting items to be delivered; and an edge-detection assembly (500, 602, 604) for detecting an edge of an item when the item is conveyed onto or discharged from the vehicle, wherein the edge-detection assembly comprises: an emitter for emitting a beam of light toward the surface and configured to form a light curtain within a detection plane,; and a plurality of detectors for detecting the beam of light, wherein an object on the surface of the vehicle affects the beam of light received by the detectors; an emitter for emitting a beam of light toward the surface and configured to form a light curtain within a detection plane,; and a plurality of detectors for detecting the beam of light, wherein an object on the surface of the vehicle affects the beam of light received by the detectors; a controller for controlling the loading of an item onto one of the vehicles or the discharge of an item from the vehicle based on signals from the edge-detection assembly, characterized in that the plurality of detectors is a linear array of photodetector, and in that the emitter is positioned below the surface so that the beam of light is projected transverse to the surface, and the edge-detection assembly (500, 606) is positioned adjacent to, but slightly below, a discharge end of the surface so that the emitter and plurality of detectors form a detection plane that is transverse and orthogonal to a plane defined by the surface.