Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
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biofuels, though more research and development is needed. Cellulosic ethanol is
produced from the structural material that comprises much of the mass of plants.
Greater deployment of flex-fuel vehicles, which can run on either conventional or
renewable fuel, and vehicles designed specifically to run on biofuels, would be
needed to increase the market penetration of renewable fuels beyond 10 percent
of light duty transportation fuel. Most vehicles on the road today can only
operate on up to a 10 percent ethanol blend. Flex-fuel vehicles are slightly less
efficient than vehicles designed to run on a single fuel. Ethanol has a lower
energy content per gallon than gasoline, requiring slightly higher volumes of
fuel. Adequate production capacity, land availability and distribution
infrastructure are also key factors for renewable fuels.
Significant work is currently underway in the area of evaluating the effectiveness
and cost of various renewable fuels in reducing GHG emissions. For example,
the EPA published an analysis of life-cycle emissions from renewable fuels in
conjunction with its revised renewable fuel standard. As such, this report to
Congress does not include detailed analysis of biofuels. Readers are instead
referred to EPA’s renewable fuels website:
http://www.epa.gov/otaq/fuels/renewablefuels/index.htm.
In the long-term (i.e., 25 years or more, with a projection year of 2050), hydrogen
offers significant potential for GHG reductions, because hydrogen fuel cells are
substantially more efficient than today’s internal combustion engines. The GHG
benefits of hydrogen depend strongly upon the method adopted for hydrogen
production, but reductions per vehicle of about 50 percent in 2030 and 80 percent
in 2050 could be realized with projected reductions in the GHG intensity of
hydrogen production. However, hydrogen will only be a viable alternative if
current technological barriers to fuel cells can be overcome. Furthermore, major
investments in new production and distribution infrastructure will also be
required to realize hydrogen’s potential. Assuming these barriers can be
surmounted, aggressive deployment could potentially lead to a 22 percent
reduction in total transportation GHG emissions in 2050, if a 60 percent light
duty vehicle market penetration could be achieved, which is the high end
discussed in current literature. Production from renewable resources, or with
carbon capture and storage (if this technology can be developed), will result in
much greater benefits than production from non-renewable sources without
carbon capture. 65
Electricity shows similarly strong potential for GHG reductions, due to the
inherent efficiency of electric motors. Electricity has the advantage of not
requiring an entirely new production and distribution infrastructure. In
addition, the cost of electricity for powering a vehicle is lower than that of
65 Vol. 2 Sec. 3.8.