Battery electric buses are already cost-competitive with fossil-fueled buses, based on their lower fuel and maintenance costs. Transit agencies around the country are starting to purchase them in bulk from companies like BYD and ProTerra.

But is electricity really cleaner than a natural gas-fueled bus? Union of Concerned Scientists tackled this question in California previously and found positive results, per UCS’s Jimmy O’Dea, and now they’ve taken their research nationwide:

We answered this for buses charged on California’s grid and found that battery electric buses had 70 percent lower global warming emissions than a diesel or natural gas bus (it’s gotten even better since that analysis). So what about the rest of the country?

You many have seen my colleagues’ work answering this question for cars. We performed a similar life cycle analysis for buses and found that battery electric buses have lower global warming emissions than diesel and natural gas buses everywhere in the country.

Here’s the UCS map:

Meanwhile, the buses are getting cheaper and better, as ProTerra’s CEO Ryan Popple explained recently to E&E News [paywalled]:

When we started out, we could really only do circulator-style routes, and we needed a fast charger for every route. That was probably five years ago, and that was because our maximum theoretical range was probably 50 miles. Now we’re regularly seeing our electric buses do anywhere between 175 and 225 miles in real service. And with all sorts of topography.

But despite the technological advancements and environmental benefits, supportive policy is still needed. Here’s the top of Popple’s policy wish list:

It is at the state of California, and it is the Innovative Clean Transit rule, the ICT. That is headed to the California Air Resources Board for an initial vote, I think, in September, and it could be fully implemented by the end of this year. What that ruling will do is set a long-term target for every transit vehicle in the state of California and a date certain by which it must eliminate its tailpipe emissions, so basically it has to become a zero-emissions vehicle… The reason it matters to us is just so that the industry can move forward with long-term planning on electric fleets.

And as more transit agencies move forward with zero-emission vehicles, we now have assurance that the clean air benefits are real — all across the country.