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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Table 3.4
Class I Railroad Fuel Usage
Railroad Activity
Total Diesel Fuel Used in 2007 (Million Gallons)
Line-Haul Operations 3,710
Yard Switching 311
Total 4,022
Source: U.S. DOT (2009).
Rail represents one of the most efficient methods of cargo transport, requiring on average
less energy and emitting fewer pollutants per ton of cargo moved than most other modes
of surface transportation (Kruse et al., 2009; VTPI, 2008). Locomotives have become about
16 percent more efficient over the last decade, and currently emit approximately 24 g
CO 2e/ton-mile (Stodolsky, 2002; SmartWay, 2009). Nevertheless, additional
improvements can be made. DOE initiated a program in 2002 to improve rail fuel
efficiency by 25 percent by 2010 and 50 percent by 2020 (relative to the 2002 base year), on
a gallons per revenue ton-mile basis (Stodolsky, 2002). Greenhouse gas emissions also
may be reduced by shifting freight from less-efficient trucks to rail; mode shift strategies
are discussed in Chapter 5 of this report.
The primary means of railroad energy use and GHG emissions through vehicle
technologies is through enhanced, more efficient power systems (Section 3.5.1). Other
strategies also can be implemented to reduce weight, improve aerodynamics, and reduce
rolling resistance (Section 3.5.2).
Power System Modifications
Overview
The primary technology-based methods for reducing emissions from locomotives involve
modifications of the power system. These may include optimization of existing diesel
systems, as well as the use of diesel-electric gensets and hybrid powertrains.
With regard to enhancements to existing diesel technologies, locomotive engines
equipped with common rail fueling systems have the ability to control and optimize fuel
injection which provides smoother, quieter running engines with better performance and
greater combustion efficiency. Conventional diesel engines inject pressurized fuel into
each cylinder at a rate dependent on the rotational speed of the engine. Common rail
injection systems allow for a more controlled fuel injection rate across all engine speeds by
storing fuel at high pressures along a common rail connected to each cylinder (MTU,
2008). High injection pressures generate very fine atomization of the fuel yielding more
efficient combustion. Furthermore, common rail systems control the point in the engine
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