The comparability of noise is not only made more difficult by subjective perception. Different weightings and special regulations between the member states also make comparability more difficult.
The Directive expects the mapping of the continuous sound level at a height of 4 metres. Measurements under these conditions are simply not feasible considering the immense effort involved. For the comparative value of the A-weighted continuous sound level for the day, evening and night time specified in the Directive, measurements would have to be taken in continuous operation, i.e. 365 days over 24 hours (365/24).