The U.S. already aims to sell only electric vehicles by 2035. Now it has a new goal: to only sell and produce zero-emissions medium- and heavy-duty vehicles like school buses and tractor trailers by 2040.

The U.S. energy secretary signed a non-binding memorandum of understanding (MOU) at the COP27 climate summit in Egypt. This agreement agrees that 30% of new medium and heavy duty vehicles, which include commercial delivery vehicles, buses and trucks, will be zero-emission by 2030 and 100% by 2040.

Under the $430 billion climate, tax and drug policy bill, signed into law in August, new commercial electric vehicles qualify for tax credits, which are up to $7,500 for light- and medium-duty vehicles and up to $40,000 for heavy-duty vehicles.

The move follows demands from a group of 16 lawmakers for President Biden to sign the agreement. The effort, led by Sen. Martin Heinrich, stressed medium and heavy trucks represent 10% of vehicles but account for 28% of total on-road greenhouse gas emissions.

“Decarbonizing commercial transport vehicles is critical to meeting our overall carbon emissions targets," Heinrich said in a statement. "By committing to this goal alongside many other nations, the United States is affirming that we are serious about meeting our responsibility on climate and protecting our children’s future."

However, lawmakers say the new memorandum "does not require U.S. federal agencies to adopt new emission standards, targets, or requirements."

Sixteen countries and over 60 state and local governments had already signed the memorandum. Manufacturers, financial institutions and other countries are expected to sign.

The move follows reports that the U.S. Environmental Protection Agency plans to issue tougher greenhouse gas emission standards for heavy-duty trucks and other vehicles through the 2030 model year by the end of 2023.

Reuters reported earlier this month the U.S. Environmental Protection Agency plans to issue tougher emissions rules for heavy-duty trucks and other vehicles through the 2030 model year by the end of 2023.