Some facts from- the clean air promotion by CEPA (Commonwealth Environment Protection Agency)

1. The average rate of increase of motor vehicles over the last 30 years was 5.2% per annum, which is more than twice the rate of growth of global population. There are now 430 million motor vehicles on earth - increasing by 9.5 million each year.
2. The Inter-State Commission estimated that, on the basis of health costs and properly damage, the cost of air pollution each year in Australian cities alone is $780 million.