6 Tier 1 Screening Assessment Process
6.1 Tier 1 quantitative screening assessment
The tier 1 screening assessment process provides simple criteria to determine whether further assessment of a project is required. These criteria are traffic thresholds and the proximity of members of the public. The tier 1 screening assessment process is outlined in Table 6-1.
A tier 1 assessment should be undertaken for all new roading projects to identify whether further assessment is required. For changes to existing roads or road networks, a tier 1 assessment should be undertaken for all roads or links where the project is likely to result in a significant increase in emissions.
Note: an air quality assessment is not necessary for any project that will not result in a significant increase in emissions at any location.
The tier 1 assessment provides screening criteria to determine whether a project requires further assessment. The basis for these criteria is discussed in Appendix 1. These criteria are intended as a guide only: the extent of the air quality assessment is a matter for judgement. For example, even if a project is well below the suggested thresholds, it may be appropriate to undertake more detailed air quality assessment in areas where there is a high level of community concern about air quality, or about new roads. The assessment will need to demonstrate that the assessment area includes all roads or links that are directly or indirectly affected by the project.
The information required to undertake a tier 1 assessment includes:
- land-use information within 50 m to determine whether people are likely to be exposed to emissions from the project − this should include consideration of likely future development, taking into account district plan provisions
- traffic information for all links and intersections affected by the project, including annual average daily traffic (AADT), level of service (or average speed), and traffic composition (for current and future conditions, where available).
6.1.1 Estimating traffic
The tier 1 assessment process relies on estimated traffic as a proxy for air quality effects. In cases where the estimated traffic is close to the thresholds described in Table 6-1, a tier 2 assessment should be considered, particularly if there are sensitive receptors such as residential houses, childcare or health-care facilities close to the proposal.
Traffic forecasts should be used to estimate traffic for the tier 1 assessment. The future assessment years may depend on the availability of traffic demand models, but should include a long-term forecast (at least 10 to 20 years). Where local traffic forecasts are not available, the default traffic growth rates provided by the Project Evaluation Manual (Transfund, 2004) should be used. If it is likely that the tier 1 traffic thresholds will be exceeded in future, then a tier 2 assessment should be undertaken.
Table 6 1: Tier 1 screening assessment for localised effects
View Tier 1 screening assessment for localised effects (large table).
6.2 Tier 1 qualitative assessment
For projects that require further assessment, it is useful to undertake a qualitative assessment of air quality issues early in the process. The main purpose of this is to identify key issues. For significant projects, a preliminary assessment may allow options to be ranked. The important point is air quality issues are identified and addressed as early as possible in the project, and a preliminary or qualitative assessment provides the opportunity to do this.
The assessment should consider the receiving environment and the nature and scale of the project. Key questions to ask include:
- Are there any facilities (residential dwellings, schools, hospitals, etc.) or sensitive receiving environments located within close proximity to the project (200 m)?
- What is the distance to these sensitive locations (or receptors)?
- Are there any locations where dispersion is likely to be poor (valleys or street canyons)?
- Are there any ambient air quality data available for the area?
- What is the level of background air quality?
- Is the proposal within a gazetted airshed?
- Will the project cause an increase in traffic volumes at any location?
- Will the project change the composition of traffic or flow dynamics at any location? For example, will existing roads linked to a new project experience an increase in the proportion of heavy traffic, or an increase in the level of congested flow?
- Is there likely to be an overall decrease in emissions compared with “do minimum” or “do nothing” scenarios?
- Is the project of sufficient scale to affect air quality across the airshed?
- Are the project scale and the degree of effect such that a detailed assessment is necessary?
