A passenger conveyor system (20) has a drive module that engages only one side (50) of the step chain loop (30). In a multiple drive module arrangement, at least one of the drive modules (40B) engages both sides (50, 52) of the step chain loop while another engages only one side (50). The inventive arrangement is not sensitive to spacing (54, 56) between the drive modules. Another example embodiment includes a synchronizing module (60) that engages both sides (50, 52) of the step chain loop (30).