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Different railroads historically assigned different meanings to the same aspect, so it is common as a result of mergers to find that different divisions of a modern railroad may have different rules governing the interpretation of signal aspects. For example, stop aspect refers to any signal aspect that does not allow the driver to pass the signal.
The signal's aspect is based on a combination of the aspects each individual head displays. Where a signal has multiple heads, aspects are read from top to bottom and are described as "X over Y over Z". Dwarf signals are smaller signals used in low-speed or restricted-clearance areas. Most signaling aspect systems have a parallel set of aspects ...
Such signals as electrically operated automatic and interlocking signals were widely adopted in the U.S. After 1908 with the advent of the Union Switch & Signal's Styles "B" & "S" and the General Railway Signal Company's universal Model 2A mechanisms manual semaphores and earlier electric disc signals quickly began to disappear.
Banner repeater signals [38] are provided on the approach to certain signals which have restricted sighting (for example because of curvature of the line, buildings, overbridges or tunnels), to give advance information of the signal aspect. Their meanings are [38] Banner on: The signal to which it applies is at danger.
Example of an L type light signal. Swiss light signals are divided into two classes, recognizable by the difference in shape of the signal: type L (for Light) and type N (for numérique (digital)). Type L was developed many years ago. The N system was developed for the Rail 2000 project and shows a clear influence of the Dutch NS'54 system. In ...
Depending on the manner in which they are used, and the nomenclature favoured by the railway administration concerned, stop signals may be further categorised as 'home signals' or 'starting signals', for example. Some stop signals are in the form of a fixed signal, generally a white board with a red solid circle.
When a crossing loop is reached, a Home Signal will have a signal for each, with the crossing segment signal being 45 degrees beneath the main line signal and in the direction of the turnout. For example, if the turnout was a right-hand the crossing signal would be on the right side below the main signal.
This type of aspect requires the driver to slow, for example, because the next signal shows a non-clear aspect (double yellow) or imposes a speed limit (yellow-green horizontal). When the train passes a signal as the driver must confirm that he saw the signal by pushing a button, otherwise the system will apply the emergency brake.