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While road-traffic noise is typically expressed as an LAeq(24h), there are several other ways of describing noise. The relationship between different metrics is not fixed, and varies with the time profile over the day. This interactive display shows the different metrics, and provides an indication of the value of each metric based on an input noise level and road type. To use this tool, first enter a noise level at the top and select a road type. Estimates of the equivalent levels using other metrics are then displayed on the right. You can click on different metrics on the right to change the graph to give a visual representation of how they are defined.

Noise metrics tool.

The metrics used in this tool are defined below. See NZS 6801:2008 for further information.

Symbol

Name

Description

LAeq(24h)

24 hour time average level

Average noise level across the entire day

Ldn

Day/night level

Average noise level with a 10 dB penalty at night (2200-0700h)

Lden

Day/evening/night level

Average noise level with a 5 dB penalty during the evening period (1900-2200h), and a 10 dB penalty at night (2200-0700h)

LA10(18h)

Daily noise level

Average of LA10(1h) measurements between 0600-0000h

LAeq(15h)

Daytime noise level (also known as Ld)

Time average noise level across the day (0700-2200h)

LAeq(9h)

Night time noise level (also known as Ln)

Time average noise level across the night (2200-0900h)

LAFmax

Maximum noise level

Maximum instantaneous noise level in a given time interval

Time profiles

The tool above is dependent on specific time profiles of traffic. The composition of traffic will vary with distance from an urban centre. As shown in the figure below, the number of heavy vehicles on the State highway network remains relatively constant, while the number of passenger vehicles decreases with distance. Heavy vehicles often travel at night, which affects the diurnal traffic patterns.

The tool uses three representative classifications of road types, with the time profile based on measurements at the following locations. It should be noted the time profile will vary from day to day at a given location, and therefore this tool should only be used for general guidance.

Road type Sample location
Strategic highway SH1, Otaki
Metropolitan motorway SH1, St Mary's Bay, Auckland
Urban arterial Bealey Avenue, Christchurch

For further information contact environment@nzta.govt.nz.

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