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

� 4.1 Summary
Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
System efficiency encompasses a diverse set of strategies that are focused on ways to
optimize the use of the transportation network by improving the efficiency of
transportation operations. These strategies seek to improve the operation of the
transportation system through reduced vehicle travel time, improved traffic flow,
decreased idling, and other efficiency of operations—improvements that can also result in
lower energy use and GHG emissions. System efficiency strategies discussed in this
report include:
• Highway operations and management strategies, including Intelligent Transportation
Systems (ITS) and other strategies that reduce congestion or otherwise keep vehicles
moving at their most energy-efficient speeds (Section 4.2);
• Truck operations and management strategies that reduce the emissions per unit of
goods moved by truck (Section 4.3);
• Improvements to the efficiency of rail and marine freight systems, including ports
and intermodal terminals, that reduce energy use per unit of goods moved by these
modes or shift freight movements from truck to those more efficient modes
(Section 4.4);
• Aviation operations practices, both at airports and en-route, that reduce fuel use and
GHG emissions from aircraft (Section 4.5); and
• Improvements in materials and methods that reduce GHG emissions generated during
the construction and maintenance of transportation infrastructure (Section 4.6).
These strategies are described in detail in the sidebar on p. 4-2. Various strategies that
improve vehicle utilization (see sidebar on p. 4-12) may also be considered forms of
improving system efficiency. For example, roadway operational improvements such as
signal priority for transit vehicles can help buses travel faster and avoid congestion,
making transit operations more efficient and encouraging travelers to shift to transit.
Ridesharing and vanpooling programs can encourage more efficient utilization of vehicles
and road space. Strategies that improve efficiency by affecting travelers’ behavior and
increasing vehicle occupancies are discussed in Section 5.0, Reduce Carbon Intensive
Travel Activity.
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