Transport emissions and travel are strongly interrelated. We have come to recognise the importance of measuring the environmental benefits of transport policies. However, we often assume that the relationships between the component emissions and travel are sufficiently complex to limit any efforts to establish broad indicators of emission impacts. This paper brings together accumulating evidence on typical emission rates per urban passenger kilometre for petrol passenger cars for a number of countries, distinguishing between key influences on emission rates such as traffic condition and vehicle weight. Given vehicle occupancy levels, we established estimates of emissions of the main air quality and enhanced greenhouse gas emissions. The emissions of interest are carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM). This paper takes the evidence on emission rates and identifies the levels of travel activity at three points in time for Sydney (1981, 1991 and 1998/99), contrasting the emission levels overall. The evidence suggests that CO has declined substantially over the 20-year period, HC and NOx have stabilised, PM10 (particulate matter in parts per million) has declined markedly, while CO2 has increased substantially. (a).
Abstract