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Other Lineside Signs

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Many signs that are visible in the railway environment are of little or no concern to train drivers and are therefore outside the scope of this website. Nevertheless, a few of the more common ones are described below, since an explanation of their purpose may be useful.

The "Limited Clearance" warning sign was introduced by British Railways in 1952. It comprises a red and white chequered board with the words "Warning - Limited clearance" (the earliest examples had the words written in capital letters). These signs are exhibited at each end of a structure close to the track. They provide a warning to any staff walking on the line that there is no position of safety along the length of the structure.

Warning - Limited Clearance
Fig. 1: "Limited Clearance" Warning Sign.

Warning - No Refuges
Fig. 2: "No Refuges" Warning Sign.

The "No Refuges" warning sign was introduced in 1979 in conjunction with the introduction of the Advanced Passenger Train (APT) on the West Coast Main Line. This sign comprises a blue and white chequered board with the words "Warning - No refuges". Originally they were only provided on lines with a permissible speed above 100 m.p.h., but this is no longer the case. Where this sign is used, a position of safety or refuges are present on the opposite side of the railway.

A "DEP" marker fitted to an overhead line electrification structure indicates that it is a Designated Earthing Point. These are usually found at intervals not exceeding 400 metres. The structures concerned are provided with earth attachment points onto which a portable earth cable may be clamped during an electrical isolation. The cable is attached or removed using an insulated pole.

DEP Marker
Fig. 3: "DEP" Marker.

Cant Marker
Fig. 4: Cant Marker.

Cant (or "superelevation") is the tilting of curved track, so that the outside rail is raised above the level of the inside rail. The degree of cant is constant throughout the length of a circular curve (i.e. a curve with constant radius). On a transition curve, however, both the radius and the cant increase or decrease regularly along the length of the curve. A cant marker is fixed to the sleeper at each 5 mm cant increment along a transition curve.

A geometry marker is attached to the sleeper where different elements of the permanent way alignment join one another.

In the example shown in figure 5, a circular curve in the direction of the upward-pointing arrow adjoins a transition curve in the other direction. Referring to a circular curve, the letters "R" and "C" mean "radius" and "cant"; in the example shown, they have values of 588 metres and 120 mm, respectively. The letters "TL" stand for "transition length", which in this case is 78 metres.

Geometry Marker
Fig. 5: Geometry Marker.

Datum Plate
Fig. 6: Datum Plate.

Datum plates are fixed to structures (platforms, bridges and overhead line masts, etc.) located near the track. The details on the plate specify the relative position of the track, which can then be monitored for movement.

Figure 6 shows a datum plate identified as chainage point number (C.P.N°) 58. The letters "DN" (on a red background) denote that the information on the plate relates to the Down line. "Offset" is the horizontal distance from the plate to the running edge ("R.E.") of the nearest rail of the relevant track, in this case 2915 mm. The track is canted at 35 mm. The top of the movable slider block is normally set at the level of the nearest rail. If it is necessary to fix the datum plate at a higher level than the track, the number above the slider block indicates the difference in height between the rail head and the slider block (300 mm in the example illustrated).

A red slider block means that the data on the plate refers to the actual position of the track at the time when the datum plate was installed. A green block denotes a track design position, to which the track should be returned in the event of it moving out of alignment.

At locations prone to subsidence, levelling posts may be placed at intervals (approximately 40 metres apart) at the side of the line. The posts are all installed at the same height alongside a straight length of track. They provide a means of visually checking for evidence of movement of the solum. By looking along the line of posts, it can be ascertained whether any subsidence has occurred.

Levelling Post
Fig. 7: Levelling Post.

Datum Point Marker
Fig. 8: Datum Point Marker (NER).

The North Eastern Railway installed datum point markers ("DP") at its passenger stations to define the precise position used for setting rates based on the distance conveyed.