The Obama administration has proposed tougher mileage standards for medium and heavy-duty trucks in hopes to reduce pollution blamed for global warming. The Environmental Protection Agency issued new rules that would lower carbon dioxide emissions from trucks by 24% by 2027 and cut fuel costs by about $170 billion over the lifetime of vehicles sold under the rule. Transportation Secretary Anthony Foxx said that the new rules would help the environment and the economy, as trucks use less fuel and shipping costs go down. Officials say the proposed standards would cover model years 2021-2027 and apply to semi-trucks, large pickup trucks, vans, buses, and work trucks. Once completed, the rules are expected to reduce greenhouse gas emissions by 270 million metric tons and save vehicle owners more than $50 billion in fuel costs, compared to previous standards.