Detailed observations of air quality and local meteorology were conducted on either side of a stretch of the Auckland southern motorway, and in the surrounding residential neighbourhood. The data revealed emissions from motorway traffic contributed, on average, to a 10% elevation in concentrations of particulate matter at a roadside site relative to a setback site (150m away or more) and to a doubling in concentrations of nitrogen dioxide. National environmental standards for air quality were not exceeded, but international health research indicates that the spatial variation in traffic-related air pollutants observed in this study represent a risk that is not currently accounted for in risk assessments in this country.
The observational data captured was used to evaluate four different roadside air quality modelling approaches. The most commonly used model in regulatory context (Austroads) was found to be conservative, but its effectiveness could be undermined by the use of inappropriate (particularly off-site) estimates of background air quality. Less commonly used assessment methods (passive monitoring, semi-empirical and regression modelling) were shown to offer several advantages for assessment.