Page:UK Traffic Signs Manual - Chapter 8 - Part 2- Traffic Safety Measures and Signs for Road Works and Temporary Situations) - Operations 2009.pdf/144

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Table 11.2 Queue length when closure reaches works – closure speed: 20 mph

Demand flow (veh/hr for each lane open through the works)	Queue length (km)
	Working window (minutes)
	3	4	5	6	7
50	0.1	0.1	0.1	0.1	0.1
100	0.1	0.2	0.2	0.2	0.3
200	0.3	0.3	0.4	0.5	0.6
300	0.4	0.5	0.6	0.8	0.9
600	0.8	1.0	1.3	1.6	1.8
900	1.2	1.6	2.1	2.5	2.9
1200	1.7	2.3	2.9	3.5	4.1

Table 11.3 Queue length when closure reaches works – closure speed: 30mph

Demand flow (veh/hr for each lane open through the works)	Queue length (km)
	Working window (minutes)
	3	4	5	6	7
50	0.1	0.1	0.2	0.2	0.2
100	0.2	0.2	0.3	0.4	0.4
200	0.4	0.5	0.6	0.7	0.9
300	0.6	0.8	0.9	1.1	1.3
600	1.2	1.6	2.0	2.4	2.7
900	1.8	2.5	3.1	3.7	4.3
1200	2.6	3.5	4.3	5.2	6.1

O11.4.6 Tables 11.2 and 11.3 show that, at this range of traffic flows, the queue is unlikely to extend beyond the point where the closure started. The tables enable the appropriate signing regime to be devised, using both permanent and temporary signs, to warn approaching traffic of the back of the queue.

11.4.7 Using a closure speed of 20 mph has the advantages that the closure start point is nearer the work site and also the length of the traffic queue is less than when a speed of 30 mph is used. However, the use of the lower speed does require vehicles approaching the rear of the queue to decelerate more sharply.

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