Page:UK Traffic Signs Manual - Chapter 4 - Warning Signs. 2013.pdf/28



Steep hills are signed using diagrams 523.1 and 524.1 together with associated supplementary plates. The gradient is calculated using the tangent of the angle concerned, although in practice it makes little difference whether the sine or the tangent is used. The gradient on new signs must be expressed as a percentage; old signs showing a ratio may remain in place until life-expired.

The sign to diagram 523.1 should normally be used only where the gradient is 10% or more. The actual gradient to the nearest whole number should be indicated on the sign, e.g. a gradient of 10.4% should be signed as 10%, but 10.6% as 11%.

On very steep or long hills where additional warning is considered necessary, the sign may be repeated as appropriate, supplemented with the "Low gear" plates shown in diagrams 525, 526 or 527. These plates must not be used alone.

The circumstances justifying the additional plates cannot be stated precisely. Traffic authorities, after consulting the police, will have to assess the need to advise drivers to engage a lower gear and gauge the likelihood of this instruction being respected. It is difficult to persuade drivers to select a lower gear to descend a long hill if their own assessment of the need is different. Where drivers have a good view of the descent and can make their own judgement, then an instruction to change gear will be obeyed only if 27