The United States Postal Service has made the most improvements in sustainability out of the major delivery companies based on several criteria. USPS has committed to ambitious sustainability goals around reducing energy use, fuel consumption, and greenhouse gas emissions. They have implemented numerous initiatives like increasing their alternative fuel vehicle fleet and optimizing delivery routes. Through these initiatives, USPS has achieved significant reductions in energy use and emissions while saving millions of dollars. However, regulators continue to push for further reductions in environmental impacts from delivery operations.