Signalogic Systems ThreeTrack

The basic crossing

The first grade crossings in North America utilized track circuits to detect trains approaching a road. A track circuit is a section of track that is electrically isolated from the rest. Using electricity, a train can be detected when it is within the limits of a track circuit because of its steel wheels which connect the two rails.

Three track circuits are used. The first one encompasses only the road itself. This is generally known as the island. The other two track circuits start adjacent to the island and extend a distance from the road. The faster the train traffic, the longer the track circuit must be to ensure adequate warning time for vehicles. These track circuits are called the approaches.

Special 'stick' circuits detect the direction of the train and thus ignore the second approach after a train goes by.

Three track crossings provide warning based on a trains position. Therefore, slow trains will cause the crossing to operate for longer times before reaching the road than fast trains.

Prototypical Three Track Crossings.

Many three-track crossings still exist in North America. Three track crossings at locations where trains do not routinely stop do not create excessive delays for traffic. More sophisticated crossing detection is costly and used only where necessary to minimize public interference.

Motion Sensing Crossings

The basic crossing

Three-Track Crossings

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