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These types of manual signaling systems typically fulfill the FRA's "signaling system" requirement for trains to exceed 60 mph. Here are some of the more common systems. Track Warrant Control In Track Warrant Control, or TWC, the train dispatcher issues "track warrants" via radio that authorize the train between two specified limits. The limits ...
Railway signalling (BE), or railroad signaling (AE), is a system used to control the movement of railway traffic. Trains move on fixed rails , making them uniquely susceptible to collision . This susceptibility is exacerbated by the enormous weight and inertia of a train, which makes it difficult to quickly stop when encountering an obstacle.
The first signals employed on an American railroad were a system of flags used on the Newcastle and Frenchtown Turnpike and Rail Road in the 1830s. The railroad then developed a more effective system consisting of wooden balls, painted red, white or black, and hoisted up or down a pole on a rope-and-pulley system.
Like the manual block systems outlined above, automatic systems divide the route into fixed blocks. At the end of each block, a set of signals is installed, along with a track-side sensor. When a train passes the sensor, the signals are triggered to display the "block occupied" aspect on the signals at either end of that block.
The first signaling systems were made possible by technology like the telegraph and block instrument that allowed adjacent signal boxes to communicate the status of a section of track. Later, the telephone put centralized dispatchers in contact with distant signal boxes, and radio even allowed direct communication with the trains themselves.
The ultimate solution to the costly and imprecise train order system was developed by the General Railway Signal company as their trademarked "Centralized Traffic Control" technology. Its first installation in 1927 was on a 40-mile stretch of the New York Central Railroad between Stanley, Toledo and Berwick, Ohio , with the CTC control machine ...
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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 North America as a "false clear") may allow a train to enter an occupied block, creating the risk of a collision. Wheel scale and short trains may also be a problem.