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

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
hybrids) may be developed. Many of these strategies have the potential to
provide net cost savings as fuel cost savings over the life of the vehicle outweigh
the higher cost of the technology. The speed of market penetration of new
technologies is limited by the turnover time of the fleet. Passenger cars and light
trucks last about 16 years on average before retirement, compared to 20 years or
more for trucks, up to 40 years for locomotives and marine vessels, and about 30
years for aircraft.
• Increased fuel economy in light-duty vehicles could reduce total
transportation GHG emissions significantly. On a per vehicle basis,
compared to a conventional vehicle, GHG reductions are 8-to-30 percent for
advanced gasoline vehicles; about 16 percent for diesel vehicles; 26-to-54
percent for hybrid electrics; and 46-to-75 percent for plug-in hybrid electrics.
• Retrofits can be used to expedite improvements. Heavy-duty trucks
retrofitted to use aerodynamic fairings, trailer side skirts, low-rolling
resistance tires, aluminum wheels, and planar boat tails can reduce per truck
GHG emissions by 10-to-15 percent. For new trucks, combined powertrain
and resistance reduction technologies are estimated to reduce per vehicle
emissions by 10 to 30 percent in 2030.
• Significant fuel economy improvements could also be realized in the rail, and
marine sectors—perhaps 20 percent per vehicle for rail and marine and 1.4-
2.3% annual improvement for aircraft during 2015-2035—through more
efficient engines and resistance reduction technologies. However, total gains
are somewhat limited due to the relatively smaller contributions of these
sectors.
Improve Transportation System Efficiency9 System efficiency strategies reduce the energy use and GHG emissions of travel
by optimizing the design, construction, operation, and use of transportation
networks.
• Lowering speed limits on national highways would generate moderate and
immediate benefits, reducing total transportation GHG emissions by up to
2 percent depending upon enforcement and compliance.
• Strategies such as traffic management and bottleneck relief—including
targeted capacity increases at points where demand exceeds capacity—have
the potential to modestly reduce GHG emissions by decreasing fuel
consumption associated with congestion and stop-and-go traffic (congestion
wastes nearly 3 billion gallons of fuel each year10). These strategies can also
9 Vol. 2, Sec. 4.
10 See “What Does Congestion Cost Us?” in 2009 Urban Mobility Report, published by the
Texas Transportation Institute.
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