A study on air pollution data has found that being in a vehicle does not necessarily protect people from pollutants outside.
Research was conducted in Auckland and Christchurch by Auckland and Canterbury universities, as well as the National Institute of Water and Atmospheric Research.
Geography professor Simon Kingham of Canterbury University said the research was conducted at peak traffic times when congestion was heavy.
He said the level of some pollutants can be just as bad as in countries such as North America or Europe, which have much higher traffic volumes.
Professor Kingham said using methods of transport other than cars is one way to reduce pollution exposure and get exercise.
The data, gathered in 2009, has just been published in an international journal called Environmental Pollution.