A number of factors can be identified as influencing the amount of emissions attributable
to the transport sector, and an effective strategy will need to take all these factors into account.
They include:
(a) the amount that vehicles are used in a given country or metropolitan area,
including the extent to which this use can be called “excessive”;
(b) the age of the vehicle fleet
and the technology used within it;
(c) the extent to which vehicles are properly maintained;
(d)
the availability of appropriate fuels and the extent to which they are used properly; and
(e)
atmospheric, climatological and topological conditions.
Four of these factors can be influenced
through policy.
(a) Excessive vehicle use.
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 kilometers travelled in developing countries is projected to average between 2.5 and 4 per cent per year between 1990 and 2030. It follows that a central question for policy makers is whether avoiding this growth is possible or desirable. A number of unknown but controversial factors affect this question, including whether growth rates of car use and those of car ownership are necessarily the same, and the extent to which transport activity drives economic growth, rather than being an indicator of it. Excessive car use is a particular and likely manifestation of excessive travel under conditions where a cultural phenomenon of car (or motorcycle) dependence develops, in combination with a number of potential price distortions that favour car use. These might include: fuel subsidies to other sectors with unintended but predictable effects on the transport sector; general subsidies to road users built into the financing of how roads are constructed and maintained, and ancillary services delivered; hidden and fixed costs in road infrastructure and land-use provision, which send unclear price signals to potential travellers; and secondary price distortions in land values that incorporate e or capitalize these other (primary) distortions.
(b) Age of fleet and technology used.
Older vehicles are associated with higher emissions of both global and local pollutants than newer vehicles, both because performance deteriorates as a function of age and because older vehicles are more likely to use obsolete, higher emitting technology.
(c) Poor maintenance of vehicles
Deterioration of emissions characteristics is linked to maintenance practices of owners, particularly for local pollutants, where catalytic exhaust after-treatment technology is used. Misfuelling of catalyst-equipped gasoline vehicles with leaded fuel, even once or twice, can seriously damage the ability of the catalyst to operateproperly, and these catalysts can also degrade over time because of other natural contaminants in fuels. Without an effective system in place to ensure that these systems are well maintained, emissions due to neglecting exhaust after-treatment maintenance are likely to increase.
(d) Unavailability or improper use of appropriate fuels.
Fuel is a factor for a number of reasons. Regulatory authorities may inappropriately specify fuel types for a given area’s conditions, leading to unnecessary emissions of certain kinds of pollutants. Vehicle owners may misfuel, out of ignorance or in response to a poorly established price signal.
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