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.
The metrics used in this tool are defined below. See NZS 6801:2008 for further information.
NZS 6801:2008 Acoustics – measurement of environmental sound(external link)
| 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 |
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, Ōtaki |
| Metropolitan motorway | SH1, St Mary's Bay, Auckland |
| Urban arterial | Bealey Avenue, Christchurch |
