A four-quadrant gate is a type of boom barrier

Boom barrier

A boom barrier is a bar, or pole pivoted in such a way as 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. Boom gates are often counterweighted, so the pole is easily tipped...

 gate protecting a grade crossing.
It has a gate mechanism on both sides of the tracks for both directions of automotive traffic. The exit gates blocking the road leading away from the tracks in this application are equipped with a delay, and begin their descent to their horizontal position several seconds after the entrance gates do, so as to avoid trapping highway vehicles on the crossing.
Four-quadrant gates are safer than two-quadrant gates, because they prevent drivers from illegally driving their vehicles around lowered gates to try to beat a train

Train

A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

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In the UK, such crossings are categorised as 'Manually Controlled Barriers' (MCB) because they are always manually controlled, usually from a signal box. Some are known as MCB-CCTV level crossings, because they are supervised by video link to the signal box from which they are remotely controlled.