correct = the "30" symbol is the maximum speed. A lower speed may be correct for the driving conditions.
you aint one of those peeps i see on the motorway in thick fog, taking the "it says I can do 70, so I will, even tho i cant see 20 feet in front of me" are you

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Certainy not, as you say within your capabilities, so if you cannot do 30 mph then it is questionable whether you should have a licence.I for one, stay within the speed limits but depending on the conditions I will always make maximum progress.