In addition to emissions that contribute to urban air pollution, the transportation sector accounts for 30% of US greenhouse gas emissions. EPA is working on solutions. For example, OTAQ'S automotive engineers are developing advanced technologies such as clean diesel combustion and hydraulic hybrids and are working with commercial partners to bring these hybrids to market. In addition, OTAQ'S voluntary initiatives are helping thousands of partners save billions of gallons of fuel - thus reducing carbon dioxide emissions - by implementing the best shipping and delivery practices and by encouraging employers to offer outstanding benefits.
http://www.fueleconomy.gov/feg//oildep.shtml (How oil dependence hurts our economy)