Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/53

DESIGN CRITERIA On dual carriageway roads the reduction of traffic speed may present difficulty. In such cases it is essential that:
 * signing is adequate and sufficient advance warning of the site is given.
 * vehicles are constrained to a single lane prior to the sampling line to reduce traffic speed to about 20mph.

Plan SV3 indicates the layout for interview sites at signal-controlled junctions. The "road narrows" sign is not used, but additional "STAY IN LANE" signs to diagram 830.3 are required on the arm of the signals on which the traffic survey is being carried out. On the other arms of the signals, a "hazard" sign to diagram 562 with supplementary plate “Census” to diagram 563 is required. These sites should be used only in built-up areas where approach speeds are low.

The principles for traffic management at survey sites differ from those in layouts in Sections D5 and D6, see paragraph D3.26.2. The principles are:

 the length of the survey area is given by the formula: (4 + 8 x the number of interviewers)(m), except when the survey site is at a traffic signal controlled junction. In this case the length is given by the formula: (4 + 4 x the number of interviewers)(m); coning to Detail C1 is used to mark a guide island through the survey site; "keep left/right" signs (610) are used on the off side behind the coning of the guide island to indicate the route traffic should take past the guide island; and to indicate the line of the traffic; and a police officer or a traffic officer is required to be in attendance as only a duly authorised officer may legally stop or direct traffic at survey sites.

The following signing is required in the primary direction on the near side upstream of the sampling point:


 * a "hazard" sign (562) with supplementary plate “Census” (563);
 * at least one “road narrows” sign (517) with supplementary plate "Single file traffic" (518);
 * a "SLOW CENSUS POINT" sign (831);
 * a "CENSUS STOP if directed" sign (830.1); and
 * a "CENSUS POINT" sign (832) located at the far end of the census point;

and in the secondary direction on the near side upstream of the first cone of the survey area:

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 * a "hazard" sign (562) with supplementary plate "Census" (563); and
 * at least one "road narrows" sign (517) with supplementary plate "Single file traffic" (518).