In a service based economy, such as the United States, transportation is the most energy consuming component. Transportation links energy use and greenhouse gas emissions. Over the last century, transportation has increased creating a host of problems, such as the increased use of petroleum. Such rises in energy use make transportation a significant contributor to the emissions of greenhouse gasses and energy use.
Andreas Schäfer from Stanford university analyzed transportation in the seminar on “Global mobility, energy use, and climate constraints,” and used passenger kilometers travelled (PKT) as a unit of analysis due to its direct relationship to greenhouse gas emissions. PKT has increased over the past 100 years but the average daily travel time has remained relatively constant because the “affordability of transportation has increased.” As GDP per capita increases, PKT increases because people use faster modes of transportation allowing them to travel further while the travel time budget remains stable.
Along with an increase in PKT, transportation has seen a rise in the average energy use per passenger, another factor in greenhouse gas emissions. An increase in energy use is in part due to structural change in travel because of more powerful vehicles and more frequent air services. Smaller households are contributing to a rise in energy use per passenger because of “the need and opportunity for sharing a vehicle has declined.” An increase in energy use per PKT results in an increase in greenhouse gas emissions.
In the past, profit driven sectors were sometimes successful in lowering energy intensity. Freight railroads, airlines, and trucks have to work towards becoming energy efficient as oil prices rise to maintain their profits. So opportunities for reducing energy intensity and greenhouse gas emissions abound. Some of the constraints of reducing gas emissions include economic efficiency, time to impact, and consumer acceptance. According to Schäfer, “the most cost effective way [to reduce greenhouse gas emissions] is imposing a CO2 tax on the entire economy.” Schäfer proposes that it is possible to reduce the energy per PKT by about 30-50% by 2025. This could be managed while maintaining performance using technology currently being developed. But, in order to effectively lower greenhouse gas emissions, “there is a need for a behavior change,” people would need to start travelling less.