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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Figure 5.1 Average CO2 Emission Rates by Mode
Source: FTA (2009).
The data on average GHG emissions by mode were used in the Moving Cooler study to
estimate the GHG reductions that are achieved through the transit services in place today.
Based on data from the National Transit Database, total GHG emissions from public
transit vehicle operations in 2007 are estimated to be 11.8 mmt CO2e. It is further
estimated that urbanized transit systems in 2007 removed 32.0 billion VMT from the
nation’s roadways, representing 1.6 percent of urban area VMT. The net effect is a
reduction of 14 million metric tons of GHG emissions. 16
Transit also has been credited with achieving indirect effects on emissions as a result of its
ability to facilitate denser, more mixed land use patterns. Such patterns result in fewer
and shorter auto trips compared to development patterns without transit and thus
reduced emissions. A recent study for the American Public Transportation Association
(APTA) estimated the average reduction of VMT per household by level of transit
availability, based on household trip data from the 2001 NHTS. This reduction was
estimated to be 2.2 VMT per household per day with access to transit (Bailey et al, 2008).
The combined GHG reduction of direct and indirect effects, accounting for emissions from
public transit, in 2007 results in a total emissions reduction of 39 mmt CO2e.
16 This figure represents the effect of the substitution of public transit passenger miles with private
automobile travel. The calculation assumes the following, based on data from the 2001 NHTS:
1) An average auto occupancy of diverted trips of 1.43, which is lower than the 1.63 average for all
trips. The 1.43 value assumes that 60 percent of transit trips are home based work with an average
occupancy of 1.14 and the remaining nonwork trips have an average occupancy of 1.84. 2) The
current auto based person miles of travel share for all trip types is 88.2 percent—i.e., 88.2 percent
of transit passenger miles are saved VMT.
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