California Governor Gavin Newsom said on Twitter that, as a result of the plan, "half of all heavy duty trucks sold in CA will be electric by 2035."

"Time to stop playing small ball," he added.

Under an executive order Newsom signed in 2020, California plans to mandate by 2045 that all operations of medium- and heavy-duty vehicles be zero emission where feasible.

The California Air Resource Board had sought waivers from the Clean Air Act to set heavy-duty vehicle and engine emission standards. California has been joined by states including Massachusetts, New Jersey, New York, Oregon, and Washington in adopting the rules.

The EPA said it is not yet approving California's request to set new regulations on pollutant exhaust emission standards for nitrogen oxide (NOx) and particulate matter for 2024 and future medium- and heavy-duty engines and vehicles.

Separately, California in August moved to require all new light-duty cars and trucks sold in the state by 2035 to be either electric or plug-in electric hybrids. California needs an EPA waiver for that regulation.

In December, the EPA finalized new emissions standards to drastically cut smog- and soot-forming emissions from heavy-duty trucks.

The new standards are 80% more stringent than current standards and EPA estimates that by 2045 the rule will result in up to 2,900 fewer annual premature deaths, 1.1 million fewer lost school days for children and $29 billion in annual net benefits.

Transportation is the largest source of U.S. greenhouse gas emissions, making up 29% of emissions, and heavy-duty vehicles are the second-largest contributor, at 23%.