
The Expert will be specific knowledgeable people at the Department of Transport, Arrive Alive Communications, the Road Traffic Management Corporation or others who might have the expertise to answer the question.
Please note that the yellow signs with black lettering and red borders (regulatory, warning, guidance, etc) are most definitely NOT "recommended" signs - they are termed "temporary" signs and are as applicable and enforceable (the regulatory signs) as their white, black lettering red border counter parts.
Yellow temporary signs are used ( or supposed to be used) to only indicate "temporary" conditions (usually for a short period of time - however, you wonder about road works that last forever) - to indicate situations and conditions which are not normal and which could be potentially dangerous.