DOT and EPA jointly proposed a rule to establish a national program to improve vehicle fuel economy and reduce greenhouse gases. The proposed program will require by model year 2016 that vehicles meet an estimated combined average emission level of 250 grams of carbon dioxide per mile and light-duty vehicle fleets will have to meet 35.5 mpg. If implemented, this program will exceed Congress' fuel economy goal of 35.0 mpg by 2020 by four years. DOT and EPA also consider these requirements to be the nation's first ever national greenhouse gas standards. DOT and EPA expect automobile manufacturers to meet these proposed standards by improving engine efficiency, transmissions and tires, as well as increasing the use of start-stop technology and improvements in air conditioning systems. They also believe that these standards will promote the use of hybrid vehicles and clean diesel engines.