Currently, environmental concerns are driving the development of new transportation fuels and vehicle technologies. The emissions from vehicles on the road are a major factor in air pollution and contribute a lot of carbon dioxide, which affects the global climate. With the increasing use of cars and trucks in the U.S., it's vital to explore new ways to power vehicles and make them more efficient. The progress made in reducing vehicle emissions and improving efficiency may not continue without big changes in how we fuel and design vehicles.