This section addresses recent patterns and trends in greenhouse gas (GHG) emissions by the transport sector, and the technological and economic potential to reduce GHG emissions. The chapter focuses on areas where important developments have occurred since the SAR. It does not attempt to comprehensively present mitigation options for transport, as was done there (Michaelis et al., 1996). For a discussion of barriers and market potential with respect to advanced transportation technologies, the reader is referred to Chapter 5, especially Section 5.4.2. For a discussion of policies, measures and options, including behavioural strategies, the reader is referred to Chapter 6.
Recent successes with key future technologies for motor vehicles such as fuel cell power trains and advanced controls for air pollutants (carbon monoxide, hydrocarbons, oxides of nitrogen, and particulate matter) seem to promise dramatic changes in the way the transport sector uses energy and in its impacts on the environment. At the same time, the rapid motorization of transport around the world, the continued availability of low-cost liquid fossil fuels, and the recent trend of essentially constant fuel economy levels caused by demand for larger, more powerful vehicles, all point towards steadily increasing GHG emissions from transport in the near future (e.g., WEC, 1998a; Ogawa et al., 1998). These are challenges that must be met by the evolution of policies and institutions capable of managing environmentally beneficial change in an increasingly global economy.
The SARs chapter 21, Mitigation Options in the Transportation Sector (Michaelis et al., 1996), provides an overview of global trends in transportation activity, energy intensities, and GHG emissions, along with a comprehensive review of economic, behavioural, and technological options for curtailing GHG emissions from the global transport sector. It concludes with an assessment of transport policies and their effects on GHG emissions. Its review of mitigation options for transportation demand management, modal structure, and alternative fuels, and its analysis of transport policies are still essentially up to date and are not repeated in this section.
Historically, transportation energy use and GHG emissions have increased because reductions in energy intensities have not kept pace with increasing transport activity. The worlds motor vehicle fleet grew at an average annual rate of 4.5% from 1970 to 1990. Over the same period, light-duty vehicle fuel economy improved by 2% per year or less. Increases in vehicular fuel economy have also been accompanied by declining vehicle occupancy rates. It is noted below that the fuel economy of road passenger transport vehicles has levelled off since the publication of the SAR, and no longer appears to be improving. Air travel and truck freight activity have also grown more rapidly than energy intensities (energy use per passenger km) have declined. Since 1970, transport energy use and GHG emissions have grown at an average annual rate of 2.4%.
The SAR concluded that by 2010 it might be technically feasible to reduce energy intensities for new transport vehicles by 25% to 50% without reduction of performance or quality, by adopting a variety of fuel economy technologies. It noted that the economic potential would likely be smaller. The adoption of energy efficiency improvements throughout the sector was estimated to be able to reduce transportation energy use in 2025 by one-third versus projected levels.
The SAR also extensively reviewed the life cycle GHG emissions from alternative fuels and concluded that only fuels derived from biomass or electricity generated from substantially non-fossil sources could reduce life cycle GHG emissions by more than 20% versus conventional gasoline internal combustion engine vehicles. Compressed or liquefied natural gas and liquefied petroleum gases are capable of reducing full fuel cycle GHG emissions by 10% to 20% over gasoline-powered light-duty vehicles, but emissions would actually increase if these fuels were used to replace diesel engines in heavy-duty vehicles.
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