Part of combating greenhouse gas emissions from vehicles will come through reducing the carbon content of fuels. This could be achieved through switching to electric cars run on a grid of renewable energy, using biofuels that have lower greenhouse gas emissions than gasoline, or other technologies that have yet to mature. It also means preventing the expansion of fuels with greenhouse gas emissions higher than conventional gasoline – gas from tar sands or oil shale, or liquefied coal.

What's clear is in order to cut greenhouse gas emissions from the transportation sector, carbon emissions from fuels will have to decrease in addition to increasing the efficiency of vehicles. But for fuel emissions reductions to be meaningful, they must be measured on a well-to-wheels lifecycle emissions basis, and the must include all greenhouse gas impacts, including indirect land use change effects.