Other Lineside Signs

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.

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 mph, 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.

Each overhead line electrification structure is fitted with a plate showing its identification number. The most common numbering convention has three components: the route code, the number of miles or kilometres from the datum point for that route, and a sequential number that identifies the individual structure within that mile or kilometre. The distance from the datum point was measured in miles until about 1972, and thereafter in kilometres. The three components of the identification number are arranged vertically on the plate.

On the structure plate illustrated in figure 3, the route code "BS" relates to the route from Birmingham (Curzon Street) to Stafford via Aston and Bescot, this structure being situated between four and five miles from the datum point, which is at Birmingham (Curzon Street). The plate's colouring conforms to the original colour scheme of the London Midland Region of British Railways, i.e. white figures on a maroon background. Modern structure plates throughout the rail network show the identification number in black on a white background.

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.

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 6, 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.

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 7 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 sites prone to subsidence, levelling posts may be placed at the side of the line at two chain intervals. 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.