A holistic analysis of passenger travel energy and greenhouse gas intensities

Transportation is a major energy consumer and emitter of greenhouse gases (GHGs). Exploring the opportunities for energy savings and GHG emissions reductions requires understanding transportation energy or GHG intensity, which is defined as energy use or GHG emissions per unit activity, here passenger-kilometres travelled. This aggregate indicator quantifies the amount of energy required or GHGs emitted to provide a generic transportation service. We show that the range of observed energy and GHG intensities of major transportation modes is remarkably similar and that occupancy explains about 70-90% of the variation around the mean; only the remaining 10-30% is explained by differences in trip distances and other factors such as technology and operating conditions. Whereas average occupancy levels differ vastly, they translate into roughly similar levels of energy and GHG intensity for nearly all major transportation modes. Understanding patterns of energy use and greenhouse gas (GHG) emissions from the transport sector can help to improve the sustainability of transportation. This study analyses the most important determinants of energy and GHG intensities for light-duty vehicles, buses, railroads and aircraft.