A barrier assembly for controlling passing of a vehicle, comprising: first and second stanchions, retention structures in the second stanchion, first and second barrier arms being pivotally connected to the first stanchion for movement between closed and open positions, wherein the first barrier arm in the closed position is spaced above the second barrier arm; the second barrier arm in the closed position is located at a selected height relative to the vehicle such that at least a portion of such passing vehicle will extend over the second barrier arm and block the second barrier arm from moving upwardly away toward the open position when the vehicle engages the first or second barrier arm, thereby preventing the first barrier arm from being moved out of a blocking position spanning between the first and second stanchions due to a structural interconnection between said first and second barrier arms (31, 34); and a retention bar connected to the distal end of the first barrier arm and oriented perpendicular to a longitudinal axis of the first barrier arm, characterized in that: the retention structures include C-shaped brackets being, when the first and second barrier arms are in the closed position, positioned slightly longitudinally away from the distal ends of the first and second barrier arms (32, 34), with bracket openings facing toward the retention bar, the retention bar being out of engagement with said C-shaped brackets and in vertical alignment with the bracket openings; the first and second barrier arms being structurally interconnected to each other only at proximal and distal end portions, wherein the first barrier arm and the retention bar are adapted so that when a vehicle crashes with sufficient force into the first and second barrier arms in said closed position, the first barrier arm bends and draws the retention bar longitudinally rearward towards the first stanchion through the bracket openings and into the C-shaped brackets such that the C-shaped brackets engage the retention bar and prevent vertical movement of the first and second barrier arms away from said closed position. first and second stanchions, retention structures in the second stanchion, first and second barrier arms being pivotally connected to the first stanchion for movement between closed and open positions, wherein the first barrier arm in the closed position is spaced above the second barrier arm; the second barrier arm in the closed position is located at a selected height relative to the vehicle such that at least a portion of such passing vehicle will extend over the second barrier arm and block the second barrier arm from moving upwardly away toward the open position when the vehicle engages the first or second barrier arm, thereby preventing the first barrier arm from being moved out of a blocking position spanning between the first and second stanchions due to a structural interconnection between said first and second barrier arms (31, 34); and a retention bar connected to the distal end of the first barrier arm and oriented perpendicular to a longitudinal axis of the first barrier arm, the retention structures include C-shaped brackets being, when the first and second barrier arms are in the closed position, positioned slightly longitudinally away from the distal ends of the first and second barrier arms (32, 34), with bracket openings facing toward the retention bar, the retention bar being out of engagement with said C-shaped brackets and in vertical alignment with the bracket openings; the first and second barrier arms being structurally interconnected to each other only at proximal and distal end portions, wherein the first barrier arm and the retention bar are adapted so that when a vehicle crashes with sufficient force into the first and second barrier arms in said closed position, the first barrier arm bends and draws the retention bar longitudinally rearward towards the first stanchion through the bracket openings and into the C-shaped brackets such that the C-shaped brackets engage the retention bar and prevent vertical movement of the first and second barrier arms away from said closed position.