boom barrier

Animation of level crossing booms lowering in Queensland, Australia. A bar gate in the Netherlands. A bar (post, pole, beam, or boom gate, also known as a boom or a boom barrier) is a beam or bar on a pivot used as a gate. The boom is lowered to block vehicular or pedestrian access through a controlled point or raised to permit such traffic. Typically, the bar has a 90° range of motion with a vertical raised resting position and a horizontal lowered resting position. Bar gates, especially manually operated ones, are often counterweighted to allow easier manual control. Bar gates are frequently paired end to end or closely offset to block traffic in both directions. Some bar gates also have a second arm which hangs 30 to 40 cm below the upper arm when lowered to increase approach visibility. This underbar typically hangs on links, so it lies flat with the main bar as the barrier is raised. Some barriers also 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 (or gamma) when raised.

Automatic bar gates