Four-quadrant gate
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A four-quadrant gate is a type of gate protecting a grade crossing. It has a gate mechanism on either side of the tracks for each direction 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 prevent vehicles from driving around lowered gates to try to beat a train.
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.
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