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

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
associated with congestion (estimated at nearly 3 billion gallons per year78). Operational efficiencies such as idle reduction, delay reduction, and more
efficient routing and scheduling can also achieve benefits in the truck, rail,
aviation, and marine sectors.
There are several sources of uncertainty in calculating the GHG benefits of
system efficiency strategies, and especially those that reduce congestion. Most
significantly, the benefits of both highway and air improvements may be offset
by induced travel demand resulting from lower travel times and costs (see
sidebar on p. 3-21). Second, the total GHG reduction benefits will decrease over
time if vehicle fuel efficiency increases beyond projected baseline levels, or the
carbon content of fuels decreases. Thirdly, construction projects result in
additional greenhouse gas emissions from the operation of related equipment
and traffic delays during the construction process, but these effects have not been
rigorously quantified and are not included in existing GHG estimates for these
strategies. Because of these uncertainties, numerical estimates are not included
for highway operations and investment strategies.
Characterization of GHG Reductions Used in this Report:
In this report, when referring to individual strategy effects, “modest” refers
to reductions in CO2e emissions of less than 0.5 percent of total
transportation emissions, or 12 mmt in 2030; “moderate” to reductions in
the range of 0.5 to 2.5 percent of total transportation emissions, or 12 to
60 mmt in 2030; and “significant” to reductions of greater than 2.5 percent
of transportation emissions or 60 mmt in 2030.
Highway traffic management strategies and real time traveler information,
including signal timing, freeway ramp metering, faster clearance of incidents,
and variable message signs, have modest potential for reducing GHG emissions;
even if induced travel demand from these projects is considered, and presuming
that these projects do not result in substantial GHG emissions from project
construction. Outside analysis suggests that widespread deployment of these
intelligent traffic management strategies could produce modest GHG benefits by
reducing inefficient vehicle operations. 79
78 See “What Does Congestion Cost Us?” in 2009 Urban Mobility Report, published by the
Texas Transportation Institute.
79 By way of example, the Moving Cooler analysis used FHWA’s Highway Economic
Requirements System (HERS) model and its embedded assumptions regarding induced
demand to estimate the impacts of traffic management strategies. This analysis
suggested that these strategies could reduce total transportation GHG emissions by as
Footnote continued
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