The Postal Service is a leader among federal agencies in sustainability efforts. In 2009, it joined with 20 international postal operators to commit to a 20 percent reduction in carbon emissions by 2020, a goal it has made significant progress toward achieving. A major contributor to greenhouse gas emissions is vehicle emissions. With the largest civilian fleet in the country – more than 213,000 vehicles – the Postal Service has both an enormous opportunity and an enormous challenge in reducing its fuel consumption. So far, the challenges have proved considerable.