Northern Railway : Train Operation during fog
Automatic Block System: In automatic signal territory, the maximum speed of a train is restricted to 30km/h during dense fog. Depending on the severity of fog, the driver is expected to control the speed of a train and restrict it further if necessary.
Absolute Block System: The maximum speed of a train is restricted to 60km/h in absolute block system territory in dense fog, and depending on the severity of fog, the driver is expected to control the speed of the train and restrict it further...
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if necessary. Further, special rules are in effect as follows:
No train awaiting line clear should be advanced beyond the starter signal.
No shunting is to be carried out on non-isolated lines in a yard after giving line clear to a train.
All IBH in semaphore signal territories are shut down and converted to single block sections for the duration of the fog.
Fog signalmen are provided to place detonators 270m in the rear of the first stop signals so as to give the drivers an audible warning of the proximity of the stop signal. (See below.)
Lime markings are made across the tracks at the signal sighting boards.
Although the final decision on the speed rests with the driver, the upper bounds of 30km/h or 60km/h help them in deciding the appropriate speed, and also allow the operating department staff make better projections in publishing the revised schedules of trains in foggy weather.
Detonators in foggy weather
Detonators are used in foggy weather or otherwise when visibility is severely impaired, to provide an audible indication to the locomotive crew that the train is approaching a signal. These detonators are flat, disc-shaped metal containers, usually coloured red, which contain an explosive mixture that detonates with the application of pressure (and therefore when the wheels of the locomotive pass over). A detonator is attached to the top of the rail using a metal clasp at the bottom of the detonator. These detonators normally have a shelf life of 7 years, although this can be extended to 10 years with annual inspections.
It is the station master's responsibility to assess whether visibility is impaired badly enough to warrant the use of detonators. At each station, there is a nominated Visibility Test Object (VTO) that is used to gauge visibility. A VTO, which must be at least 180m away, may be a post specially erected for this purpose, with a lamp for the night; or the arm (during the day) and backlight (at night) of a semaphore signal; or the light of a fixed colour light signal (day and night). If the VTO is not visible, then it is necessary to use detonators on all running lines of the station.
Detonators are placed in pairs - 10m apart - at a distance of 270m in the rear of the signal to be protected, which is usually the outermost signal on the approach to a station (in double distant territory, the detonators are placed 270m to the rear of the inner distant signal). Usually, fog signal posts are erected to mark the locations. Recently [11/04] IR has begun erecting shelters by the side of the track as well, for the benefit of the staff who have to stay there to replace the detonators as each train passes by.
The detonators have a safety radius of about 45m; staff must remain outside this distance from the detonators when they explode, to avoid injury; and locomotive crew also take care not to lean out of the cab on approach to stations when there is a possibility that detonators may be in use.
Deploying the detonators is considered a critical safety-related activity, hence the station master is authorized to call on all available staff for this, even off-duty staff if necessary. During prolonged foggy periods or if there are not enough station staff, the permanent way gangs can also be pressed into service for this.