California state legislators have introduced a bill proposing a law that would phase out diesel trucks in the US’s most populous state in an effort to control pollution and greenhouse gas emissions.

However the action will likely face major opposition from truck and transport companies and other businesses that transport products in big rigs.

The bill, by state senator Nancy Skinner, would direct the California Air Resources Board to require a 40 per cent reduction in diesel emissions by 2030 and an 80 percent reduction by 2050, cuts that experts say would not be possible without a major overhaul of the trucking industry.

Heavy- and medium-duty buses and trucks make up seven per cent of the vehicles on California’s roads but contribute 20 per cent of the heat-trapping carbon emissions spewed into the atmosphere, according to the Union of Concerned Scientists, a nonprofit science advocacy organisation.

They also produce 33 per cent of the state’s nitrogen oxides, a major ingredient in particulate matter, or smog.

“While California is a leader in climate protection, we still have very dirty air,” said Senator Skinner, pointing out high rates of asthma, lung and heart disease and other respiratory problems in low-income communities like Oakland and Richmond, which are near freeways and the Port of Oakland.

“We’ve got rising rates of asthma, which is caused by smog and particulate matter, which primarily comes from diesel.”

The bill would also designate an unspecified amount of money from the state’s Greenhouse Gas Reduction Fund for the development of alternate fuels and technology.

It is the latest move by California to take control of its own greenhouse gas emissions as the Trump administration pushes for lower fuel efficiency standards and promotes the oil and gas industries.

Truck operators and drivers are naturally not as keen on the proposed law

General manager of the North Bay Truck Centre in California, Jim Buell, said that compared with gas engines, diesel engines are much more powerful, last longer — they can last 1.2million km, a gasoline engine about 400,000km — and generally get 30 per cent better fuel economy.

“I don’t think the technology has come far enough to phase out diesel, so I don’t see how it’s possible,” said Buell, whose company maintains and repairs trucks.

“It would be a big strain on the industry and it would absolutely affect our business. Every truck I’m looking at in my yard now is diesel.”

The proposed law would join other recent moves designed to help the state meet its goal to cut carbon emissions to 1990 levels. Former Gov. Jerry Brown signed legislation last year requiring all of California’s electricity to be from clean sources, such as solar, wind and hydropower, by 2045. The San Francisco Municipal Transportation Agency recently committed to replacing its diesel- and gas-powered buses with an all-electric transit fleet by 2035.

Skinner’s bill follows a ruling in December by the California Air Resources Board requiring all transit agencies to make their fleets entirely emission-free within two decades. The rules prohibit the purchase of any new gas- or diesel-powered public transit buses by 2029 and require all buses to be emission-free by 2040. It means some 14,000 gas-guzzling public buses will be taken off the streets as they get old and replaced with battery and fuel-cell electric vehicles.

Environmental groups believe the gradual phasing out of diesel trucks and buses will give electric vehicle manufacturers time to design, build and purchase clean-fuel replacement rigs.

“The technology for zero-emission vehicles is accelerating at a rate that is pretty breathtaking,” said Kathryn Phillips, director of Sierra Club California, who says at least six factory and assembly facilities are working on clean trucks and buses. “I believe the technology is such that, in a decade or two, there will be no more need for diesel trucks to be on the California market.”

Tom Howard, fleet director for Veritable Vegetables in San Francisco, which uses delivery trucks, said there have been significant improvements in electric, hydrogen fuel cell, compressed natural gas, propane, and plant- and food-based fuels.

Still, he said, it will be a tall task for manufacturers to fully replace diesel and for California to build enough infrastructure so that truckers can keep their big rigs going. The move to all but eliminate diesel trucks in California would prevent truckers from elsewhere from entering the state.

“Business would essentially stop without some type of a diesel engine fuel that can be burned,” Howard said. “You’re talking tractors, forklifts, cranes. I just don’t see diesel going away. That fuel is 200 years old and it’s not going to be replaced in 30 years.”

Skinner’s proposal falls in line with the California Global Warming Solutions Act of 2006, which designated the state Air Resources Board as the agency that would monitor and regulate emissions of greenhouse gases. The Air Resources Board already requires truck owners to install diesel exhaust retrofits that capture pollutants and replace engines older than the 2010 model year by 2022.

Skinner’s bill would require the board to develop a market-based strategy by  1 January, 2021, to bring the trucking industry into compliance with federal ambient air quality standards.