1.9.1
and
1.9.2
. Where a range is quoted for siting distance
in column 4, progressively larger figures should be used for 85th percentile speeds towards the higher
end of the speed range, to compensate for the greater braking distance. Braking distance will also be
affected by gradients, and siting distances may need to be increased on steep hills, e.g. an increase of
50% might be made for a 10% descent. Special considerations apply to the signs listed below:
(i) When used on single carriageway roads:
Diagram 563, when indicating “Blind summit” or “Hidden dip”, might need to be placed further from the
hazard than shown in column 4 of the first table to allow for a hidden vehicle approaching at speed
(ii) When used on high‑speed dual carriageway roads:
Diagram 510 “Roundabout ahead” – see
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