The Environmental Noise Directive requires noise levels to be assessed from road traffic, railways, major airports and industry.  It is not a requirement to assess noise generated by other activities, such as may arise from gardening, construction work, sports and leisure activities, pop concerts and the like.

Noise maps produced for the Environmental Noise Directive represent the annual average noise levels at a height of 4 metres above the local ground level.

The Environmental Noise Directive requires noise levels to be assessed in terms of Lden and Lnight.
Lden is the equivalent continuous noise level over a whole 24-hour period, but with noise in the evening (19:00 to 23:00) increased by 5 dB(A) and noise at night (23:00 to 07:00) increased by 10 dB(A) to reflect the greater noise-sensitivity of people at those times.
Lnight is the equivalent continuous noise level over the night-time period (23:00 to 07:00). Lnight does not contain any night-time noise weighting.

The UK government has published a procedure that allows LA10 (18-hour) levels to be converted into Lden and Lnight values.  Because motorways carry a higher proportion of traffic at night compared with other roads, the conversion factors for motorways are different from the conversion factors for other roads.