Author(s)：Jaesung Choi, David C. Roberts
A variety of research fields has analyzed actual productivity change from environmental pollution through the Malmquist environmental productivity index, but to our best knowledge, no research has thus far been conducted in the transportation sector to evaluate the effects of a CO2 emissions change on actual productivity. For this reason, this study reviews how actual productivity in the US transportation sector has been affected by the CO2 emissions change for 2002-2012 and then reveals the driving forces behind it. We find that a CO2 emissions increase from 2002 to 2007 has a negative effect on actual productivity in the US transportation sector, but the CO2 emissions reduction for 2008-2011 increases actual productivity. A state mainly showing a sustainable growing pattern (decrease in CO2 emissions and increase in actual productivity) experiences a higher technological innovation increase than an efficiency decrease. This finding suggests that using fuel-efficient and carbon reduction technologies as well as alternative transportation energy sources may be essential factors to both grow transportation and prevent global warming.
Figure 1 shows the changes in gross domestic product (GDP) and CO2 emissions from 2002 to 2011 for the US transportation sector  . The increasing trend in US CO2 emissions remained until 2007, but thereafter
they fell compared with the period of 2002-2007. Although the US experienced a global financial crisis at the end of the 2000 s, the US transportation sector grew consistently after a slight decrease in 2009, so that CO2 emissions reduction entered a new phase.
Figure 2 shows CO2 emissions changes in the transportation sector by state for 2002-2011 . During the period 2002-2011, 32 states among 51 emitted CO2 in 2011 less than in 2002, but 19 states increased CO2 emissions in 2011 compared with in 2002. The top five largest CO2 emissions reductions between 2002 and 2011 arose in California, Michigan, Pennsylvania, Louisiana, and Ohio, but the top five largest CO2 emissions increases occurred with Illinois, Florida, Georgia, South Carolina, and Iowa. However, as noted, since 2008, all states excluding Nebraska, North Dakota, and South Dakota have decreased CO2 emissions.
It can be assumed that CO2 emissions reduction efforts in the transportation sector have a negative effect on productivity growth since reducing CO2 emissions would lead to not only a decrease in fossil fuel consumption (mainly used to all transport modes), but also large-scale financial investments for developing CO2 reduction technology and alternative energy.
This study, nevertheless, could not estimate the individual and quantified effect on actual productivity of a change in environmental policy, fuel-efficient and CO2 reduction technology development, or each input used. We could only decompose actual productivity change into efficiency and technological changes based on the Malmquist environmental productivity index, but those two factors might be two of many more possible driving forces. In addition, due to data confidentiality, this study had no choice but to focus on aggregate transportation sector data, not by each transport mode such as airlines, trucks, railways, sea vessels, pipelines, and so on. Thus, those limitations might be solved by a future study, if one can collect data by transport mode and use a multiple regression.
See also: Comments to Paper