August 28, 2025. Last calendar year marked the fifth consecutive year that commercial fleets in the State of California fueled by Bio-CNG (renewable natural gas, or RNG) achieved a carbon-negative transportation outcome, according to a report released by The Transport Project (TTP) and RNG Coalition alongside partner California Renewable Transportation Alliance (CRTA).
Renewable natural gas accounted for 99% of all on-road fuel used in natural gas vehicles in California in 2024, driven by the state’s successful Low Carbon Fuel Standard (LCFS) program. According to data from the California Air Resources Board (CARB) the annual average carbon intensity score of bio-CNG in that mix was -194.13 gCO2e/MJ.
In fact, Bio-CNG holds the lowest average carbon intensity of any clean fuel option on California’s roadways today and is the only fuel producing a negative carbon intensity fleet outcome in the California Low Carbon Fuel Standard (LCFS) Program, which includes ethanol, biodiesel, renewable diesel, bio-CNG, bio-LNG, electricity, alternative jet fuel, and hydrogen.
Even more, while RNG made up just 5.6% of all on-road alternative fuels dispensed by volume under the California LCFS in 2024, it generated 22.5% of all carbon dioxide equivalent (CO2e) emission reductions of on-road alternative fuels reported.
Captured above ground from organic material in agricultural, wastewater, landfill, or food waste, RNG can produce carbon-negative results when fueling on-road vehicles like short- and long-haul trucks, transit buses, and refuse and recycling collection vehicles.
“When used as a transportation fuel, RNG displaces gasoline and diesel in applications that are difficult – if not virtually impossible – to electrify,” said Daniel Gage, President of The Transport Project. “Renewable natural gas offers the most immediate, cost-effective, and scalable way to deploy clean trucks and buses and significantly reduce greenhouse gas and criteria pollutants… and it does so without upending existing business operations.”
TTP and RNG Coalition report that in 2024 a total of 220.87 million gallons (DGE) of natural gas were used as motor fuel in the state. Of that, 218.68 million gallons (DGE) were from renewable sources. Even more, rapidly increasing amounts of RNG motor fuel used in California are produced in state; 23.21% in 2024 versus just 6.74% in 2021, and the overwhelming majority is from agricultural operations.
“Renewable Natural Gas (RNG) continues to decarbonize heavy-duty trucking in California and beyond amid historic growth of RNG facilities across North America,” said RNG Coalition’s Sam Wade, VP of Public Policy. “On the demand side, RNG use in California has grown 44% over the last five years, displacing millions of tons of greenhouse gas emissions and generating more reductions than any other clean fuel under California’s Low Carbon Fuel Standard. With 99% of natural gas vehicles in California already operating on RNG, the challenge before us is to accelerate the conversion of diesel engines to those fueled by RNG, so these benefits are extrapolated across all medium- and heavy-duty fleets in the State, and beyond.”
In addition to their negative greenhouse gas (GHG) emissions, ultra-low NOx medium- and heavy-duty RNG-fueled trucks and buses perform at levels that are 90% below the federal nitrogen oxide (NOx) standard and 90% below the federal particulate matter (PM 2.5) standard. NGVs virtually eliminate criteria pollutant emissions that contribute to asthma, heart disease, and poor air quality.
Investing in RNG-fueled trucks and buses provides policymakers the most cost-effective way to achieve significant emissions reductions from commercial transportation sources today. With $100 million in grant funding covering the full price of new clean vehicle purchases, investing in RNG-fueled Class 8 trucks delivers six times more greenhouse gas and two times more criteria pollutant emissions reductions than deploying similar battery electric trucks. If $100 million in new truck grants covered just the incremental truck purchase cost over legacy diesel, RNG investments deliver 12 times more greenhouse gas and 3.5 more criteria pollutant emissions reductions than battery electric, deploying 1,333 RNG trucks versus just 357 battery electric trucks.