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Section 30: Signs associated with Engineering Possessions

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When a portion of railway line is closed for engineering work, it is said to be under "absolute possession". These possessions are usually pre-arranged. Although the line under possession will be blocked to normal traffic, engineering trains may be required to enter and move within the possession. Normal signalling is suspended inside a possession and all movements are under the control of a designated person, now known as the "Person in charge of the Possession" (PICOP). A possession is usually protected by a series of three detonators placed on one rail. A red banner flag or board by day or a steady or flashing red lamp at night was placed at the middle of the three detonators. In addition, the stop signal approaching the possession would be held at 'danger'.


A change to the Rule Book in 1985 introduced the concept of the "work site", which is under the control of an Engineering Supervisor. It is permissible (but not mandatory) to set up one or more work sites within a possession. Double-sided marker boards are placed at the limits of a work site. On the original design of marker board, one side showed flashing blue and red lights [30.1], indicating entrance to a work site. This could not be passed without the Engineering Supervisor's authority. The other side had flashing blue and white lights [30.2] and indicated exit from the work site. This could not be passed without the authority of the PICOP.

[30.1] Work Site Marker Board (entrance to work site).
Area: All Areas except LMR and SR   Usage: High   Status: Historical
[30.2] Work Site Marker Board (exit from work site).
Area: All Areas except LMR and SR   Usage: High   Status: Historical

From January 1986, the lights in the marker boards were altered in colour. The side indicating entrance to a work site now has two flashing red lights [30.3] and the side indicating exit from a work site shows two flashing yellow lights [30.4]. Marker boards were introduced on the London Midland Region and Southern Region at that time.

[30.3] Work Site Marker Board (entrance to work site).
Area: All Areas   Usage: High   Status: Current
[30.4] Work Site Marker Board (exit from work site).
Area: All Areas   Usage: High   Status: Current

The possession limit board was introduced in the Doncaster area in 1993 to replace the red banner flag, board or lamp formerly provided at the detonator protection. It comprises a red octagonal board with the word "stop" and a red light which may be either steady or flashing [30.5]. The board, which is double-sided, is placed in the 'four-foot', alongside the middle of the three detonators. They were subsequently adopted for use throughout the network.

[30.5] Possession Limit Board.
Area: All Areas   Usage: High   Status: Current

In 2002, a trial was undertaken involving an experimental board [30.6] being positioned at certain signals nominated as protecting signals for an engineering possession. The sign, which resembled an ordinary stop board (see [26.15]), carried the wording "All drivers must personally contact the signaller for authority to proceed" to reinforce the requirements of the Rule Book.

[30.6] Possession Protecting Signal Reminder Sign.
Area: Great Western Zone   Usage: Medium   Status: Historical

Special arrangements apply when engineering work takes place at an interface between Network Rail and Channel Tunnel Rail Link (CTRL) infrastructure. In addition to the usual protection arrangements, a double-sided demarcation board is placed at the infrastructure boundary. The front of the board, facing the Network Rail infrastructure, has "CTRL" [30.7] and the rear of the board has "NR" [30.8]. No movement may pass the demarcation board without the authority of the supervisor responsible for the work site beyond it.

[30.7] Demarcation Board (front).
Area: NR/CTRL Interfaces   Usage: Medium   Status: Current
[30.8] Demarcation Board (rear).
Area: NR/CTRL Interfaces   Usage: Medium   Status: Current