CONTACT CENTRE WAIT TIMES: Our Contact Centre is currently experiencing significant wait times. View frequently asked questions

SCAM ALERTS: Report a phishing scam or learn about the latest phishing emails

ROAD USER CHARGES (RUC) DISCOUNT: Find out more about the temporary RUC reduction scheme

ONLINE SERVICES: We are currently experiencing issues with all our online services at the moment. We are working to resolve the services as soon as possible. We apologise for any inconvenience caused.

COVID-19 SERVICES UPDATE: Information on Waka Kotahi services, extensions and more

ONLINE SERVICES: We currently have an issue with receiving some payments and are working to resolve this issue as quickly as possible. We apologise for any inconvenience.

EASTER WEEKEND – PLAN AHEAD: Heading away for the long weekend? Check our holiday journeys tool(external link)

SCAM ALERTS: Refund email and Vehicle licence (rego) renewal phishing emails

CONTACT CENTRE WAIT TIMES: Our Contact Centre is currently experiencing significant wait times. View frequently asked questions

CONTACT CENTRE PHONE LINES: Our Contact Centre phone lines are currently unavailable. View frequently asked questions

Background air quality is the level of contaminant across the airshed from all sources. This includes contributions from natural sources (eg volcanoes, forest fires, wind-blown dust, etc) and from human-generated sources (eg industry, domestic heating and ‘remote’ roads).

Background air quality is used to assess the cumulative impact of a discharge to air. In the case of a roading project, the air pollution coming from the road being improved (the relative impact) needs to be added to the background concentration of air pollution (ie background air quality excluding nearby roads) to allow the cumulative (or absolute) impact of the project to be calculated.

The Transport Agency has developed default background air quality values by census area unit. This information can be used as an input into an air pollution dispersion model, like the Agency’s Air Quality Screening Model to estimate the cumulative impact. These default values are provided in the background air quality  map(external link) (below) and in the background air quality data spreadsheet [XLS, 266 KB] (a full version of the spreadsheet is available upon request from Information on how these values were derived is available in the Background air quality for NZ Transport Agency state highway assessments [PDF, 1 MB] technical report.

The Transport Agency has released a draft Background air quality guide [PDF, 3.3 MB] on applying these default values to project assessments and how to assess whether predicted air quality impact from a road project, combined with background air quality, is likely to result in air quality standards or guidelines being exceeded.

In order to reduce uncertainty and comprehensively assess the air quality effects of a roading project, the default background air quality values may need to be supplemented with more site-specific information.  Suitable data may be available from regional councils, the Transport Agency or research organisations.  However, projects with a high air quality risk, typically large projects in major urban centres, may require a dedicated monitoring campaign to to determine background air quality.

Please note the following section of content is possibly being delivered from an external source (IFRAME in HTML terms), and may present unusual experiences for screen readers.

For further information contact