President Barack Obama on Tuesday will order his agencies to tighten the fuel-efficiency standards for medium- and heavy-duty vehicles, the latest stage in his effort to tackle climate change without waiting for Congress to act.

During a visit Tuesday morning to a Safeway distribution center in Upper Marlboro, Md., Obama will announce he’s directing the Environmental Protection Agency and the Transportation Department to develop fuel-efficiency and greenhouse gas standards for future trucks and other heavier vehicles by March 2016. They would cover vehicles for model years after 2018.

Tighter post-2018 standards for heavy-duty vehicles, which account for about a quarter of onroad greenhouse gas emissions from the transportation sector, were part of the list of items Obama laid out in June in his climate action plan. The new requirements follow up on standards the administration imposed three years ago for heavier vehicles from model years 2014-18.

The initial standards were meant to reduce fuel use and emissions by 10 to 20 percent from vehicles like school buses, garbage trucks, large pickups and tractor-trailers, and the White House said they will save a total of 530 million barrels of oil and cut greenhouse gas emissions by 270 million metric tons over the vehicles’ lifetimes. The White House would not immediately say how steep the cuts would be from the post-2018 standards.

Under Obama’s order, EPA and DOT should issue an initial notice of proposed rule-making by March 31, 2015, according to a White House fact sheet.

The new vehicle standards build upon efficiency requirements the administration approved during Obama’s first term for passenger vehicles, which must get an average of 54.5 miles per gallon by 2025, as well as sweeping greenhouse gas regulations that EPA is working on for power plants.

As part of Tuesday’s announcement, EPA and the National Highway Traffic Safety Administration must work with manufacturers, states, labor groups and others on developing methods to cut fuel consumption and emissions after the 2018 time frame. The agencies will also work with the California Air Resources Board “with the goal of ensuring that the next phase of standards allows manufacturers to continue to build a single national fleet.”

Obama will also tell the Energy Department to offer assistance to any company that joins the National Clean Fleets Partnership, a public-private partnership that encourages companies to switch to alternative or advanced vehicles. Those companies will get “specialized resources, technical expertise and support in developing a comprehensive strategy to reduce fuel use and achieve greater efficiency and cost savings.”

The program’s members include Coca-Cola, UPS and Waste Management, and together operate about 1 million commercial vehicles in the U.S., according to the White House.

Obama isn’t focusing entirely on executive actions on Tuesday. He will also repeat his call for Congress to set up an Energy Security Trust Fund, an idea the president has called for in his past two State of the Union addresses.

His plan would use drilling revenue to fund a research and development program for advanced vehicle technologies. But it faces serious opposition from congressional Republicans because it does not include expanded oil and gas drilling.

Obama will also call on Congress to revive the expired tax credit for producers of cellulosic biofuel and will propose Congress create a $200 million “tax credit to catalyze investment in the necessary infrastructure to support deployment of advanced vehicles at critical mass,” the White House said. The credit would be fuel neutral.

The White House will release a report Tuesday touting the administration’s work on fuel economy and vehicle emissions issues and detailing these new actions.

The transportation sector is the second largest source of greenhouse gas emissions in the U.S., after electric generation.