An autonomous transport vehicle includes a frame forming a payload section configured to hold one or more pickfaces, a transfer arm movably mounted to the frame, a drive section connected to the frame, and a controller connected to the drive section, the controller being configured to effect an on-the-fly sortation of pickfaces carried by the autonomous transport vehicle according to a predetermined case out order sequence where the controller commands the drive section so that two or more pickfaces are picked from one or more first case unit holding locations and placed at one or more different second case unit holding locations according to the predetermined case out order sequence.