Visibility

What it measures

How far ahead you will be able to see at this section, in whole miles or kilometres, such as 6 mi or 10 km. Fog, heavy rain, blowing snow, dust, smoke and spray all bring it down.

Why it matters on the road

Visibility is the one reading that shortens the time you have rather than the grip you have. At the lowest of these thresholds there are seconds, not minutes, to react to a stopped vehicle. Choose a speed that lets you stop within the distance you can see, and use dipped headlights in fog.

How it is marked

A mark describes this reading alone and does not change the section’s rating. Fog itself rates a section at least CAUTION; see Severity.