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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
engines are available for heavy-duty vehicle use, including delivery trucks, school and
shuttle buses, and recycling trucks (Propane Council, 2009).
LPG stations can be found throughout the country. There were over 2,200 LPG fueling
stations nationwide, as of June 2009, making it the most widely available alternative fuel in
the United States today (U.S. DOE, 2009b).
In marine applications LPG-powered vessels have been used as a replacement for
relatively small (from 5 to 60 horsepower) gasoline-powered vessels. Due to the lower
energy content of LPG, there is a 10 to 15 percent power loss at high-speed especially
under load; therefore, it is not an effective alternative fuel for freight movement. Similarly,
LPG is not an option for rail modes.
Magnitude and Timing of GHG Reductions
Life-Cycle Emissions
Unlike natural gas, propane does not have a significant direct global warming potential
when released into the atmosphere, although it does have indirect impacts. 22 A report by
Argonne National Laboratory (ANL, 1999) combined emissions data from three primary
studies to determine the effects of LPG on LDV emissions. These results were used in the
GREET model for a comparison with LDVs running on gasoline. The analysis found that
LPG reduced GHG emissions by 21 to 24 percent (including a methane emissions increase
of 10 percent). The cited GHG reductions are for LPG produced from natural gas. For the
current industry average LPG supply (60 percent produced from natural gas, 40 percent
from crude oil), GREET 1.8b estimates GHG reductions of 17 percent for LPG vehicles
compared to gasoline vehicles. As with natural gas vehicles, GHG levels associated with
LPG are roughly comparable to those from diesel vehicles; therefore, use of LPG in heavyduty
vehicles is not analyzed as a GHG reduction strategy.
Market Penetration
The EIA’s short-term outlook for LPG production predicts fairly constant levels over the
next few years. U.S. natural gas liquids production (of which over 95 percent is LPG) is
22 Indirect global warming potential (GWP) occurs through the affect on terrestrial radiation
absorption by influencing the formation and destruction of tropospheric and stratospheric ozone,
or by affecting the absorptive characteristics of the atmosphere. Propane is estimated to have an
indirect GWP of 3.3 (IPCC, no date). To the extent that LPG vehicle use leads to fugitive propane
emissions associated with additional production, storage and/or distribution, some amount of
GHG enhancement may be expected. However, the life cycle approach adopted for this analysis
only includes direct GWPs.
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