The following description was taken from NTC: Carbon dioxide emissions intensity for new Australian light vehicles 2018 :

This information paper provides detailed data on the carbon dioxide emissions intensity performance of new passenger and light commercial vehicles sold in Australia during 2018.

This report focuses on vehicle emissions performance, measured in terms of grams of carbon dioxide per kilometre (g/km). This is a measure of vehicle efficiency or intensity rather than a measure of actual vehicle emissions, which depends on many factors such as distance travelled, the nature of the driving and road and traffic conditions. Fleet-wide vehicle emissions depend on many factors including consumer preference (for example, vehicle type, engine size and power, fuel type and transmission type). Consumer preferences can also be influenced by government policies and regulations, industry influence and fuel prices.