Colorado and major automakers have reached a deal on the state's plan to adopt California's zero-emission vehicle (ZEV) requirements after earlier talks had ended without agreement.

Reuters said the state, which plans to join the California programme starting in the 2023 model year, had agreed to allow automakers to earn credits for selling electric vehicles in the two model years prior and use other transitional credits available in other states.

Two major auto trade groups representing 99% of US car and truck sales, including General Motors, Volkswagen, Toyota Motor and Hyundai Motor, said the state agreed to address concerns "by providing the support Coloradans need to buy electric vehicles while allowing auto manufacturers to transition into Colorado's ZEV programme."

Reuters noted California had led the way in challenging the Trump administration's plans to roll back Obama-era environmental regulations. Last week, that state struck a deal with four major automakers to tighten emissions rules, bypassing the Trump administration's effort to strip the state of the right to fight climate change by setting its own standards.

The Colorado agreement must be approved by the state's Air Quality Control Commission at a meeting later this month, the news agency noted.

In June, Colorado said talks with major automakers had failed to reach a deal on voluntary efforts to boost electric vehicle sales. The automakers explored a deal after meeting with Colorado Governor Jared Polis in April.

Polis in January signed an executive order directing the state to adopt California's ZEV rules, joining nine other US states: Connecticut, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Rhode Island and Vermont.

The California ZEV mandate, first adopted in 1990 and revised on numerous occasions, requires the sale of an increasing number of electric vehicles or other zero-emission vehicles.

Last year, California forecast that about 8% of the state's new vehicle sales in 2025 would be zero-emission and plug-in electric hybrids.

In August, Reuters noted, the Trump administration proposed freezing fuel efficiency standards at 2020 levels to the end of 2026 and barring California from imposing its own vehicle emission rules or setting requirements for zero emission vehicle sales. The administration was expected to finalise that regulation this autumn.

But California and 18 other states, including Colorado, said they would fight the Trump administration's freeze in court, a legal battle that could leave automakers in regulatory limbo for years.