A conveyor comprising: drive sprockets and idle sprockets; a conveyor belt trained around the drive sprockets at a downstream end of the conveyor and the idle sprockets at an upstream end and driven by the drive sprockets along a carryway at a first speed in a direction of belt travel from the upstream end to the downstream end, the conveyor belt including: an outer conveying side and an opposite inner side; a plurality of article-supporting rollers extending outward of the outer conveying side and the opposite inner side and arranged to rotate on axes perpendicular to the direction of belt travel; a plurality of flights disposed at spaced apart locations along the length of the conveyor belt, the flights each including an actuating element extending outward of the inner side of the conveyor belt and a stop movable between a retracted position at or below the level of the rollers extending outward of the outer conveying side and a blocking position extending outward from the outer conveying side to a level above the level of the rollers; an activation belt underlying the conveyor belt in a portion of the carryway and providing a mobile bearing surface contacting the rollers and the actuating elements of the flights at the inner side of the conveyor belt; wherein the activation belt is configured to advance in the direction of belt travel at a second speed greater than the first speed to cause the flights to move into the blocking position and the rollers to rotate opposite to the direction of belt travel on the conveying side to push articles supported atop the rollers opposite to the direction of belt travel against the stops in the blocking position. drive sprockets and idle sprockets; a conveyor belt trained around the drive sprockets at a downstream end of the conveyor and the idle sprockets at an upstream end and driven by the drive sprockets along a carryway at a first speed in a direction of belt travel from the upstream end to the downstream end, the conveyor belt including: an outer conveying side and an opposite inner side; a plurality of article-supporting rollers extending outward of the outer conveying side and the opposite inner side and arranged to rotate on axes perpendicular to the direction of belt travel; a plurality of flights disposed at spaced apart locations along the length of the conveyor belt, the flights each including an actuating element extending outward of the inner side of the conveyor belt and a stop movable between a retracted position at or below the level of the rollers extending outward of the outer conveying side and a blocking position extending outward from the outer conveying side to a level above the level of the rollers; an activation belt underlying the conveyor belt in a portion of the carryway and providing a mobile bearing surface contacting the rollers and the actuating elements of the flights at the inner side of the conveyor belt; wherein the activation belt is configured to advance in the direction of belt travel at a second speed greater than the first speed to cause the flights to move into the blocking position and the rollers to rotate opposite to the direction of belt travel on the conveying side to push articles supported atop the rollers opposite to the direction of belt travel against the stops in the blocking position. an outer conveying side and an opposite inner side; a plurality of article-supporting rollers extending outward of the outer conveying side and the opposite inner side and arranged to rotate on axes perpendicular to the direction of belt travel; a plurality of flights disposed at spaced apart locations along the length of the conveyor belt, the flights each including an actuating element extending outward of the inner side of the conveyor belt and a stop movable between a retracted position at or below the level of the rollers extending outward of the outer conveying side and a blocking position extending outward from the outer conveying side to a level above the level of the rollers; an activation belt underlying the conveyor belt in a portion of the carryway and providing a mobile bearing surface contacting the rollers and the actuating elements of the flights at the inner side of the conveyor belt; wherein the activation belt is configured to advance in the direction of belt travel at a second speed greater than the first speed to cause the flights to move into the blocking position and the rollers to rotate opposite to the direction of belt travel on the conveying side to push articles supported atop the rollers opposite to the direction of belt travel against the stops in the blocking position.