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

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
resulting economic benefits from reduced congestion and travel times, whether
by highway, transit, air, or rail. The primary exception is speed limit reduction,
which reduces mobility and may increase shipping costs by increasing travel
times. Land use and transit strategies reduce household transportation expenses
and have mobility benefits for those who do not drive because of advanced age,
young age, disability, or income. Finally, public health benefits can result from
land use, nonmotorized, and transit strategies that encourage walking and
biking.
For fuels strategies, the environmental and social impacts of biofuels production
could be negative for those production pathways that require considerable
amounts of land and compete with food supplies. Also, to the extent that fuels
are produced domestically rather than from international sources, national
security benefits may be achieved due to the reduced threat of energy supply
disruption.
Travel activity strategies may have significant cobenefits or disbenefits. The
most significant benefits result from improved mobility from improvements to
alternative modes, including transit, ridesharing, and nonmotorized travel, as
well as more compact land use patterns that support these alternatives. There
can also be opposition to increased densities at the local level. The most
significant disbenefits include mobility and equity impacts to lower-income
populations from pricing strategies that increase the cost of carbon-intensive
travel beyond their willingness or ability to pay without compensating increases
in availability of less carbon-intensive, more affordable travel ammentities or
other compensation mechanism. Pricing also faces substantial barriers in the
form of public opposition and concerns over equity impacts, which may be
addressed through redistribution of revenue and/or investment in alternative
modes.
Many strategies reduce air pollution, but the reductions would vary depending
upon the specific strategy. Wind and weather patterns also complicate the
impacts. Reductions in total vehicle activity would reduce air pollutant
emissions. More efficient vehicle operations (reduced idling, congestion, etc.)
would further reduce air pollutant emissions beyond the levels from vehicle
activity reduction, though NOx emissions would likely increase with speeds
above 40-45 mph. Heavy-duty and off-road vehicles tend to have less strict
emission controls than light-duty vehicles, however, so some strategies that
reduce GHG emissions through switching travel or goods movement to more
efficient modes (transit, freight rail, marine) may not reduce emissions of all
pollutants, and may even increase some emissions (although Federal standards
for heavy-duty vehicles and locomotives are leading to substantial
improvements in these sectors). In some cases, localized benefits may be far
more significant than the total quantity of pollutants reduced in a region.
Vehicle fuel efficiency strategies may reduce air pollutant emissions by reducing
the amount of fuel burned. However, emission standards would be the primary
factor influencing emissions levels. Some technologies (such as hybrid-electric
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