| Supervisor: | The person, usually situated in the closure control vehicle, who is responsible on site for the co-ordination of the entire closure operation. |
| Traffic-free zone: | The section of carriageway ahead of the closure that is clear of traffic. |
| Working area: | The area of a carriageway in which works activities take place. |
| Working window: | The time during which the working area is free from non-works traffic. |
O11.3THE PRINCIPLE OF THE TECHNIQUE
O11.3.1 A mobile carriageway closure is created by a number of specially-signed vehicles, usually one per lane, that manoeuvre within normal free flow traffic conditions to align laterally across the carriageway, (Plan MCC1a). Their speed is then gradually reduced to a predetermined speed, thereby slowing the traffic behind them. This will create a traffic-free zone between the closure vehicles and the traffic in front of them. It is the speed differential between traffic moving away in front of the closure and the closure itself that creates the working window.
O11.3.2 When the last of this downstream traffic has passed the proposed working area, (Plan MCC1b),work on the carriageway can commence in a traffic-free environment.
O11.3.3 The convoy closure vehicles move towards the working area travelling at an agreed reduced speed (from 20 mph to 30 mph) and when they reach the working area, (Plan MCC1c), work on the carriageway must have ceased and the carriageway must have been cleared for the passage of traffic. When the closure vehicles have passed the working area, they resume normal speed and move to the left-hand lane of the carriageway to allow traffic to pass. The operation is then complete.
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