Car account for ______ the greenhouse gases in the US.

Cars account for half the oil consumed in the U.S., about half the urban pollution and one fourth the greenhouse gases. They use the same oil as other industrial nations and in the cities of the developing world. As vehicle use continues to increase in the coming decade, the U.S. and other countries will have to deal with these issues or else face unacceptable economic, health-related and political costs. It is unlikely that oil prices will remain at their current low level or that other nations will accept a large and growing U.S. contribution to global climatic change.
     Policymakers and industry have four options: reduce vehicle use, increase the efficiency and reduce the emissions of conventional gasoline-powered vehicles, switch to less harmful fuels, or find less polluting driving systems. The last of these -- in particular the introduction of vehicles powered by electricity is ultimately the 0nly sustainable option. The other alternatives are attractive in theory but in practice are either impractical or offer only marginal improvements. For example, reduced vehicle use could solve traffic problems and a host of social and environmental problems, but evidence from around the world suggests that it is very difficult to make people give up their cars to any significant extent.