An apparatus for sorting a plurality of items, comprising: a plurality of sort destinations; a plurality of delivery vehicles (400, 604) for delivering items to the sort destinations, wherein each vehicle comprises: a surface for supporting items to be delivered; and an edge-detection assembly (100, 402, 404) 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 (104, 304) for emitting a beam of light toward the surface, wherein the emitter is positioned below the surface so that the beam of light is projected transverse the surface; and a plurality of detectors (106, 306) 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 plurality of sort destinations; a plurality of delivery vehicles (400, 604) for delivering items to the sort destinations, wherein each vehicle comprises: a surface for supporting items to be delivered; and an edge-detection assembly (100, 402, 404) 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 (104, 304) for emitting a beam of light toward the surface, wherein the emitter is positioned below the surface so that the beam of light is projected transverse the surface; and a plurality of detectors (106, 306) 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 for supporting items to be delivered; and an edge-detection assembly (100, 402, 404) 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 (104, 304) for emitting a beam of light toward the surface, wherein the emitter is positioned below the surface so that the beam of light is projected transverse the surface; and a plurality of detectors (106, 306) 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. an emitter (104, 304) for emitting a beam of light toward the surface, wherein the emitter is positioned below the surface so that the beam of light is projected transverse the surface; and a plurality of detectors (106, 306) 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.