The days of buses that run on diesel or natural gas are officially numbered in California. The California Air Resources Board — the state’s clean air agency — voted on a new rule that will require cities to shift to 100 percent electric buses.

Though the various transit agencies have already shown their commitment to electric buses, officials are hoping the new rule — which will prevent the various cities’ transit agencies from buying non-electric buses — will move things along faster.

The new rule will only apply to transit buses — meaning privately owned buses and school bans are not included — and will be rolled out over time. The first wave will begin in 2023, during which the agencies will be forced to buy electric buses 25 percent of the time. The number will double to 50 percent in the following year and, by 2029, agencies will no longer be able to buy non-electric buses.

In a statement to Fast Company, Adrian Martinez — a staff attorney at the nonprofit Earthjustice — explained why rulings like this are so important.

“The rule is necessary because it sends a clear market signal that the fifth largest economy in the world is serious about zero-emissions transit buses,” Martinez said. “Even though you’ve had a lot of transit agencies step up to the plate to commit to 100 percent, getting the stamp of approval from a state as big and as powerful as California is important to send a signal nationally.”

California has led plenty of actionable changes that will help our climate. It’s believed that California could be the first state to ban plastic straws from restaurants, and they previously voted to replace three natural-gas power plants with the world’s largest battery system. In 2006, the Golden State set strict targets to reduce its greenhouse gas emissions to 1990 levels by 2020 — and achieved those goals four years ahead of its target. Proving that the state has no intentions of slowing down, Governor Jerry Brown recently signed a landmark bill that will aim to derive 100 percent of the state’s electricity from clean energy sources by 2045.

As Gov. Brown said in a press release about the bill, “It will not be easy. It will not be immediate. But it must be done.”