Conclusions

Reducing Greenhouse Gas Emissions From U.S. Transportation

By combining a variety of policies, U.S. transportation-related carbon emissions could be cut by 20 to 25 percent by 2015 and by 45 to 50 percent by 2030, in comparison to a continuation of current trends in energy efficiency, petroleum dependence, and traffic growth. Curbing the growth of transportation's GHG emissions will require a combination of meaningful policies and technological progress. A successful policy portfolio will involve all modes of transportation and will include a variety of measures, from fuel economy and fiscal policies to infrastructure investments. In the longer run, technological progress — and policies that promote it — must provide the means for continued efficiency improvements and ultimately for a transition to low-carbon energy sources for transportation. There are many specific forms of policies that can achieve the same objective.

Reducing transportation's GHG emissions will not be easy because demand for mobility of both people and goods will almost certainly continue to grow. Increasing transportation activity will result in growing energy use and GHG emissions, unless the energy efficiency of vehicles can be increased, alternative energy sources developed, and ways found to improve the ability of land use and transportation systems to provide accessibility with less motor vehicle travel.

The international effort to protect the global climate, especially efforts to reduce GHG emissions from transportation, provides a unique opportunity for the United States to work cooperatively with other countries to reduce worldwide demand for oil. Both near-term and longer-term actions to reduce GHG emissions from transportation will produce major benefits for U.S. energy security in the form of reduced oil imports and reduced economic losses from oil price shocks. Actions to reduce GHG emissions taken in concert with the other oil-consuming nations of the world will undermine the market power of the OPEC cartel, amplifying the United States' own efforts to increase energy security. By staying out of the global effort to reduce GHG emissions, the United States may be squandering its best chance to solve the oil dependence problem.

Harnessing market forces is a very useful but probably insufficient strategy for mitigating transportation's GHG emissions. Even a carbon cap-and-trade system, as beneficial as it would be, would be hindered by the tendency of households to undervalue fuel economy. It would be unlikely to bring about an appropriate level of investment in long-term transportation energy technologies and would not guide important investments in transportation infrastructure and the built environment. A combination of policies is needed to promote energy efficiency, stimulate investments in research and development, improve land use and infrastructure planning, and harness market forces.

For at least the next decade, the U.S. transportation system will continue to be powered primarily by conventional, petroleum-based liquid fuels. As a result, the most productive options to reduce GHG emissions will be fossil fuel or carbon pricing policies, energy efficiency improvements, and the blending of low-carbon replacement fuels with petroleum liquids.

Over the next 15 to 30 years, new technologies will be introduced, and the stock of transportation vehicles will be turned over twice, making much larger increases in energy efficiency possible. The world is also likely to have begun an important transition from conventional petroleum to alternative energy sources. The path of least resistance would be a gradual transition to increased use of unconventional sources of liquid hydrocarbon fuels, yet promising technologies are emerging that could lead in a very different direction, toward major roles for hydrogen and electric motors. It is not too soon to begin planning for and developing the technologies for an energy transition for transportation. The use of unconventional fossil fuels entails higher costs and more severe environmental consequences. An alternative, cleaner, more economically efficient energy future for transportation is possible, if the right technologies can be developed.

Increasing the efficiency of energy use now will buy more time for the transition and for the development of alternative technologies. Other decisions made over the next 10 years in R&D and also in infrastructure investments will influence the path taken. The paths that lead toward very low GHG emissions will require bold changes in technology and investments in infrastructure. At the same time, continued improvements in energy efficiency will be valuable whichever path is chosen. If the high-carbon fossil fuel path is chosen, continuing efficiency gains will be needed to hold carbon emissions in check. If the low-carbon path is chosen, higher efficiencies will help reduce the costs of clean technologies.

An attractive alternative to a petroleum-based transportation system is one based on hydrogen. Hydrogen can be produced from a variety of energy resources with minimal environmental impacts with the right technologies. Hydrogen, however, is not yet ready to compete with petroleum. Technological advances are needed in hydrogen storage, in the robustness and cost of fuel cells to produce power from hydrogen, and in economical and environmentally benign hydrogen production. The federal government's newly created FreedomCAR and hydrogen initiatives and California's Fuel Cell Partnership aim to create a transportation system powered by pollution-free hydrogen fuel cells. Even with the best efforts of these programs, it will be at least 15 to 20 years before hydrogen can achieve significant success in the marketplace.

The United States is the source of one-fourth of the world's GHG emissions. It is also the owner of the world's largest transportation system, the fastest growing source of CO₂ emissions in the U.S. economy. The U.S. transportation system is a key target for GHG emissions reduction. There are many responsible and cost-effective actions that can be taken to restrain the growth of GHG emissions from transportation. Action can begin today, and pathways exist to a low-carbon future for transportation. Formulating and implementing an effective, comprehensive strategy will not be easy, but it can be done.