WASHINGTON, D.C. — Two federal agencies are jointly proposing new standards for medium- and heavy-duty vehicles — including school buses — that would increase fuel efficiency and decrease carbon pollution.

The proposal comes from the U.S. Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA). Agency officials said that the proposed standards are expected to lower CO2 emissions by about 1 billion metric tons, cut fuel costs by about $170 billion, and reduce oil consumption by up to 1.8 billion barrels over the lifetime of the vehicles sold under the program.

“Once upon a time, to be pro-environment you had to be anti-big-vehicles. This rule will change that,” U.S Transportation Secretary Anthony Foxx said. “In fact, these efficiency standards are good for the environment — and the economy. When trucks use less fuel, shipping costs go down.”

According to the EPA and NHTSA, medium- and heavy-duty vehicles currently account for about 20% of greenhouse gas emissions and oil use in the U.S. transportation sector, but they only account for about 5% of vehicles on the road.

The proposal announced on Friday builds on the Phase 1 fuel efficiency and greenhouse gas emissions standards that are already in place for model years 2014 to 2018.

The proposed Phase 2 vehicle and engine performance standards would cover model years 2021 to 2027. They would apply to semi-trucks, large pickup trucks and vans, and all types and sizes of buses and work trucks.

School buses fall under the category of vocational vehicles. The agencies are proposing new CO2 and fuel consumption standards for vocational vehicles starting in model year 2021, with increased stringency in model year 2024 and a fully phased-in stringency level in model year 2027.

The fully phased-in Phase 2 standards for vocational vehicles would reportedly achieve up to a 16% reduction in CO2 emissions and fuel consumption compared to Phase 1. The agencies project that the vocational vehicle standards could be met through improvements in the engine, transmission and driveline; lower rolling-resistance tires; idle-reduction technologies; and weight reduction.

Cummins, a key supplier of engines for large school buses, expressed its support for the federal agencies' proposed rulemaking.

"Cummins welcomes the proposal with its goals to improve fuel efficiency and reduce GHG [greenhouse gas] emissions, creating a win-win for both customers and the environment," said Dave Crompton, president of the company's engine business unit. "We are pleased that the new proposal builds upon the Phase 1 framework that aligns technological advances and industry success."

A public comment period will be open for 60 days after the proposal is published in the Federal Register. Also, NHTSA and the EPA will host two public hearings and will continue to meet with stakeholders during the comment period.

For more information on the proposal, go to this EPA web page or this NHTSA web page.