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Provision of Permissible Speed Signs

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Permanent Speed Restrictions and Maximum Permissible Speed

In the beginning, locomotives were not equipped with speedometers and lineside speed signs were only installed by exception. The locations of any permanent speed restrictions (P.S.R.s) were detailed in appendices to the working timetables, latterly issued as a separate document called the "Sectional Appendix". Drivers relied heavily on their own experience and familiarity with the railway to be able to judge their speed and observe any speed restrictions.

Outside of those specific locations where permanent speed restrictions were in force, no upper speed limit was specified until after the Second World War, when each railway line was assigned a "maximum permissible speed" as was laid out in the relevant appendix. The maximum permissible speed was not necessarily constant along the whole length of the railway. Usually, no lineside speed sign was provided at places where it increased or decreased.

Following a fatal derailment at Sutton Coldfield on 23 January 1955, British Railways made a decision to extend, throughout its entire network, the former LNER practice of installing lineside speed signs at the beginning of all permanent speed restrictions.

Figure 1
Fig. 1: Permanent Speed Restriction.

Normally, no sign was installed at the end of a P.S.R. (i.e. at the place where maximum permissible speed may be resumed), except where one P.S.R. was immediately followed by another of a different speed.

Figure 2
Fig. 2: Abutting Permanent Speed Restrictions.

On lines where the maximum permissible speed was 90 m.p.h. or higher, speed signs were provided at the end of every speed restriction. Drivers would therefore see a lineside speed sign at each place where the permitted speed changed. This formed the basis of what was termed "continuous route signing", which aided route learning. Current practice is to install a speed sign at every location where the permitted speed changes, irrespective of the upper limit. The term "continuous route signing" is no longer used, however. Sectional Appendices issued from the 1990s onwards make no distinction between maximum permissible speed and permanent speed restrictions, and present a continuous picture of permitted speeds along the railway.

Railways that operate exclusively with cab signalling are not provided with lineside speed restriction signs, except where required for degraded operation.

Diverging Lines

A speed restriction sign applicable to a diverging line is fitted with an arrow sign pointing left or right as appropriate. A single sign with two arrows is provided if there are equal speed divergences on both sides in close proximity. Signs were not generally provided at junctions between parallel lines or at the entrance or exit of loops or platform lines, etc., where a standard speed restriction of 15 m.p.h. applied unless otherwise indicated.

Figure 3
Fig. 3: Permanent Speed Restrictions on Diverging Routes.

If there was also a reduction in speed on the straight route commencing at the diverging junction, a separate sign was installed about 40 yards on approach to the sign for the diverging route.

Figure 4
Fig. 4: Permanent Speed Restrictions on Diverging Route and Straight Route.

Since 1996 it has been practice to site the two signs side by side.

Figure 5
Fig. 5: Permanent Speed Restrictions on Diverging Route and Straight Route.

Converging Lines

A memorandum issued by the British Railways Board's Director of Operations in 1988 outlined an enhanced form of continuous route signing, a feature of which was the provision of a reminder sign where a converging line joined a higher speed route. Reminder signs, which are usually of miniature form, do not denote a change of permissible speed for drivers proceeding straight along the higher speed route, in which case they may be disregarded.

Figure 6
Fig. 6: Permissible Speed Reminder Sign for Converging Line.

Non-standard Differential Speed Restrictions

'Non-standard differential' speed restrictions indicate a variation to the permissible speed, applicable only to the type of train denoted by letters on the relevant signs (e.g. "HST" for High Speed Trains, as in the examples that follow).

Figure 7 illustrates an earlier method of signing non-standard differential speeds. Under this method, a distinctive commencement sign (coloured yellow) is installed at the start of each portion of line where a higher speed applies. A commencement sign may be co-located with an ordinary P.S.R. sign (as shown at "A") or installed independently (as shown at "B"). On passing a commencement sign, drivers of HSTs may disregard any ordinary signs indicating a lower speed, including any further signs ahead (as shown at "C"). Ordinary speed restriction signs indicating a higher speed continue to apply. The higher speeds apply until a termination sign is reached; this can either be installed independently or co-located with an ordinary P.S.R. sign (as shown at "D").

Figure 7
Fig. 7: Non-standard Differential Speed Restrictions.

Figure 8 illustrates the same piece of railway as figure 7 but in this example the non-standard differential speeds are signed in accordance with current standards. In addition to having a different appearance, the manner in which these signs are provided also differs. Crucially, they do not override any subsequent signs indicating a lower speed, hence the need for a second "HST70" sign co-located with the "50" sign at "C" and also the absence of a termination sign at "D".

Figure 8
Fig. 8: Non-standard Differential Speed Restrictions.