How are non-interlocked (NI) stations operated?

July 16, 2019, 12:15 PM
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Non-interlocked stations are what their name implies: there is no interlocking of any kind. The points have to be set appropriately and locked manually before pulling off a signal. The station master is personally responsible for ensuring that this is done and is supposed to have the keys to unlock the points with him or under his control. Trains are restricted to 15km/h over station limits. Non-interlocked stations are found only on sections with very light traffic. The most basic version of non-interlocked stations have truly no arrangement for controlling the points in relation to the signals and rely entirely on the signalman or station master. Sometimes some simple mechanisms are used that provide some minimal safeguards without providing true interlocking.

Padlocked points are common at non-interlocked stations. Here, facing points are equipped with a clamp or through bolt that has a padlock that can be used to lock the points in position. To operate the points, the station master has to hand over the key for the padlock (unless the station is small enough that the station master can walk over and operate the points himself). The key is usually handed over with a badge or token indicating the route to be set, to minimize any misunderstanding in the verbal instructions. Obviously, the procedure takes time and depends on a human element for safety. The locking arrangement on the points is essential; it is not enough to just lock the lever that operates the points.

Key Locking: In this system, each set of points has a pair of keys. When the route is set one way, one of the keys is freed and the other must remain inserted at the points; when the points are set for the other route, the first key must be inserted and the other key is freed. The station master keeps the free keys in a glass-fronted box so that he can tell at a glance which routes have been set. Although this system ensures that routes are set and locked for a particular line, it does not ensure that the points have been set properly, and there is no interlocking between the signals and the points. Points may be damaged (e.g., by being trailed through) and the station master has no indication of this if he just relies on the keys in his possession. Badges or tokens are handed out as in the case with padlocked points. Key locking used with facing points (but without any real interlocking or the provision of bracketed home signals) is occasionally termed Rudimentary Interlocking in IR’s materials.

Source – IFRCA.org

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