气候变化领域集成服务门户

For all the economic and social benefits that it confers, the U.S. ground transportation system is not sustainable. This non-sustainability derives from both the fuel (oil) used to power transportation and from the ever increasing congestion that threatens ever worsening gridlock. Oil is a finite resource whose consumption leads to air pollution, the emission of greenhouse gases such as carbon dioxide, and increasing threats to national security from growing imports. Congestion stems from the confluence of three factors: urban designs that are nearly totally dependent on motor vehicles; a growing population that is resulting in an increasing number of drivers; and a fixed supply of major urban roadways. A continuation of current trends would result in a society ever more locked in congestion and burdened with increased emissions of greenhouse gases and growing threats to national security. An alternative vision is offered, one where vehicles run off renewable energy sources and have no pollution or greenhouse gas emissions and where alternative transportation modes meet a much larger fraction of mobility needs.