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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
In practice, however, the potential for mode-shifting appears limited. Due to handling
costs, rail and marine are generally only competitive for long-haul movements (at least
500 to 1,000 miles), and for relatively low-value goods for which speed and reliability are
less of a concern. Furthermore, most of the energy efficiency benefits are lost for shorter
movements due to the need to transfer goods to truck at one or both ends of the journey.
Operational improvements in the aviation sector show moderate potential for GHG
reductions. Air traffic modernization measures that are underway or planned through the
Federal Aviation Administration’s NextGen program (for example, allowing airplanes to
fly on more direct routes) could potentially reduce annual GHG emissions from aircraft by
2.5 to 6 percent through 2035. Additional benefits of up to 10 mmt CO2e annually could
potentially be achieved by measures to reduce aircraft delay at airports, and 2-3 mmt CO2e
annually through more efficient or alternative fuel airport equipment and operations.
Improvements may also make air travel faster and less expensive, representing a benefit to
travelers. Overall demand for air travel is forecast to increase, offsetting at least some of
the GHG reduction benefits. The magnitude of this offset has not been estimated.
Transportation infrastructure construction and maintenance practices also show
potential for modest to moderate reductions in GHG emissions. Perhaps the most
significant currently available strategy is the use of fly ash or other recycled materials in
cement, a proven technology that has the potential to reduce GHG by an additional
15 mmt CO2e annually. Use of warm- and cold-mix asphalt has the potential to reduce
GHG by about 3 mmt CO2e annually, but research on the application of these technologies
in the U.S. is still in progress. Other actions by transportation agencies also have the
potential to contribute modestly to GHG reductions. These include the use of alternative
fuels in transportation agency vehicles and equipment, reduced idling of construction
equipment, and increased energy efficiency in transportation agency buildings. These
actions are estimated to provide benefits of about 2-3 mmt CO2e per year.
Cumulative Benefits
The effects of the individual strategies presented in this report are generally independent
of each other, and therefore can be added together to provide a rough estimate of
cumulative savings from these strategies. Benefits are shown (see Table 4.1) separately for
highway modes and for non-highway modes (air, rail, and marine). Highway strategies
include trucks and construction practices, as well as general roadway management and
operations. Combined benefits of all strategies are estimated to range from 2.9 to
5.7 percent of total transportation emissions in 2030, with the majority of the benefits from
the highway sectors. Separate benefits estimates for 2050 are not presented, as these
strategies can generally be fully implemented by 2030.
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