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As an alternative to the insulated joint, audio frequency track circuits can be employed using a tuned loop formed in approximately 20 m (66 ft) of the rail as part of the blocking circuit. Some insulated joints are unavoidable within turnouts.
A rail break between the insulated rail joint and the track circuit feed wiring would not be detected. Failure modes that result in an incorrect "track clear" signal (known usually in the US as a "false clear") may allow a train to enter an occupied block, creating the risk of a collision.
For example, the CRT may be reached due to a removal of a rail section or an Insulated Block Joint (IBJ). A stressing engineer measures the rail section to be removed and places indicators with marks on the foot of the rails. After the rail section is cut out, its first stress free temperature is determined.
A signal in the Flushing–Main Street station. Most trains on the New York City Subway are manually operated. As of 2022, the system currently uses automatic block signaling, with fixed wayside signals and automatic train stops. Many portions of the signaling system were installed between the 1930s and 1960s.
Double junction, or level junction (left hand running). A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that carries traffic through the junction at reduced speed.
The work entails replacing 8,000 rail ties, 1,600 feet (490 m) of rails, and insulating rail joints. Repairs will also be made to mud spots, drainage and rail anchors, along with replacing bridge timbers on the Noroton River Bridge and resurfacing the entire line.
A segment of ballastless track. A ballastless track or slab track is a type of railway track infrastructure in which the traditional elastic combination of sleepers and ballast is replaced by a rigid construction of concrete or asphalt. Ballastless track of the type "Low Vibration Track" in a turnout in the Gotthard Base Tunnel 's Faido ...
Automatic block signaling (ABS), spelled automatic block signalling or called track circuit block (TCB[1]) in the UK, is a railroad communications system that consists of a series of signals that divide a railway line into a series of sections, called blocks. The system controls the movement of trains between the blocks using automatic signals.