This chapter first provides a broad overview of strategies to make travel more energy efficient and identifies areas of uncertainty that research could address. It then indicates areas in which research is needed and describes criteria for how such research should be organized and managed.
As an organizing scheme, it is useful to think about reducing transportation GHG emissions and energy consumption on the basis of a framework initially developed by Schipper et al. (2000) and employed by Eads (2008). The amount of CO2 emissions from fuel combustion by transport can be represented as follows:
G = CO2 emissions (or GHG emissions) from fuel combustion by transport,
A = total transport activity,
Si = modal structure of transport activity,
Ii = energy consumption (fuel intensity) of each transport mode, and
Fi,j = sum of GHG emissions characteristics of each transport fuel used by various modes (i = transport mode, j = fuel type).
Understanding the potential value of mitigating transportation GHG emissions and reducing energy consumption requires examination of each of these variables.
A = total transport activity, which is a function of growth in gross domestic product (GDP) and population. It is also influenced by development and trade patterns (which determine the distance between origins and destinations).
S = modal structure of transport activity. Strong growth has occurred in recent decades in aviation, in the freight mode share of trucks compared with rail and water, and in light-duty vehicle (LDV) (cars, SUVs, and pickup trucks used for personal travel) use compared with transit.