Road work speed limit signs

As a regular driver in Spain I have noted the increased vigilance of the authorities in enforcing speed limits and traffic laws with some recent reductions in road fatalities/caualties. I always try to adhere to the set speed limits and I've noticed the improvements in this area of other drivers, particularly where speed cameras are located. However, there is one area where I have found that other drivers seem to flout the posted speed limits and that is where the yellow and red speed limit signs are in force where there are road works and/or road surface problems and the speed on the motorways is usually gradually decreased to 80kmh. Even where there are speed cameras in existence other drivers seem to ignore these red and yellow signs, which appear to be compulsory.

Can anyone inform me whether these signs are compulsory or advisory. I always understood that signs with a red outer ring were compulsory but the attitude of other drivers suggetss otherwise. I have tried to research online but there's little information.

Thanks

As far as I'm aware, they are compulsory, but very much ignored by most people. I'm also a driver who likes to stick to the speed limit (more or less) but some of the roadwork speed signs are a bit rediculous. They seem to have a standard procedure for putting these signs up which is something like 80 - 60 - 40 - 20.

20kmh??? I'm not surprised people don't abide by this one, especially when it looks like the roadworks have either come to a standstill through lack of funds (always seems to happen) or they have finished and just not got round to taking the signs down (also always seems to happen). They also cover up signs with bin liners which then get blown off and leave people confused about what the actual speed limit is....Are we now under the rules of the yellow signs or the white ones as we can see both? Apart from the usual confusion as to whether the yellow ones are relevent or not, I think the Spanish take even less notice of the yellow ones than they do the white ones.