THE CONVOYING METHOD
O9.11.1 The basic principles of convoy working are the same for all works situations. On single carriageway roads, the choice between single and three-vehicle working will depend on the traffic flow and the characteristics of the site. The single-vehicle method will be more appropriate when flows are low and there are convenient locations for turning round at each end of the works.
O9.11.2 The way in which these principles are applied is dependent on the number of convoy vehicles used, the ease with which these vehicles can be turned round after they have led traffic through the site, and whether the convoy system is being operated on a unidirectional or a shuttle basis. The main methods of working have been set out in the paragraphs which follow. The drawings are diagrammatic and are not to scale. R indicates "red" or "stop", and G means "green" or "go". Yellow/grey vehicles are convoy vehicles.
SLIP ROAD MERGES
O9.11.3 Experience has shown that the convoy system can be used successfully at slip road merges. In such cases, the following procedure is substituted for Step 3 of "Dual carriageway – multiple-vehicle working sequence" below. When the end of the queue passes the signal head, the traffic control supervisor switches the main carriageway signals to red. Another convoy vehicle takes up position on the main carriageway to prevent unrestricted vehicles from travelling through the site and at the same time, the traffic control supervisor changes slip road traffic signals to green, enabling the slip road traffic to join the end of the previous convoy. When the slip road queue has passed, the slip road signals are switched to red and the convoy vehicle which has been blocking the main carriageway moves forward to a position to prevent all unrestrained vehicles from the main carriageway and slip road from travelling through the site.
O9.11.4 If it is not considered appropriate to operate convoy working on the main carriageway on dual carriageway roads, an alternative method of working is to divert all traffic from the main carriageway at the interchange (see Part 1: Design, Section D6.20). Traffic rejoins the main carriageway via the entry slip road and convoy traffic management on the slip road is used to control the traffic past the works on the main carriageway. Queuing traffic on the slip road should not be permitted to extend onto the interchange and cause congestion.
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