Level of activity or vehicle use is an important factor to
take into account in the overall analysis of transportation emissions, particularly in those cases
where long-run solutions are envisioned to help avoid the development of a problem. In a
number of developed countries (where data and information are more readily available), studies
have shown that growth in activity has either significantly increased the amount of CO2 emitted
in the sector or substantially dampened the reduction of CO2
emissions that would have occurred,
the latter because of efficiency improvements during the last three decades of the twentieth
century. In the absence of a policy to address vehicle use, growth in vehicle kilometres travelled
in developing countries is projected to average between 2.5 and 4 per cent per year between 1990
and 2030.