1.Boom barrier gate, also known as a boom gate, is a bar, or pole pivoted to allow the boom to block vehicular access through a controlled point. Typically the tip of a boom gate rises in a vertical arc to a near vertical position.
2.Boom gates are often paired either end to end, or offset appropriately to block traffic in both directions.
3.Some boom called fence boom, have a second arm which hangs 300 to 400 mm below the upper arm when lowered, to increase approach visibility, and which hangs on links so it lies flat with the main boom as the barrier is raised.
4.Some boom called articulated boom, feature a pivot roughly half way, where as the barrier is raised, the outermost half remains horizontal, with the barrier resembling an upside-down L when raised.