If you read the article ... there are several already in SF in testing. The news was that a 4th bus maker has been added to the test crew (3 buses each from 3 builders so far). Some have been out in regular service. See these Youtubes for example:
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Then, SFMTA complaining that they need greener bus yards: [
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And, SF isn't the only place. AC Transit - [
www.youtube.com] The UC shuttle between the Sacramento hospital and the Davis campus has been using an electric bus since before the pandemic.
LA area has a bunch of them. Foothill Transit was a pioneer, complete with overhead charging at a large transfer/layover point midway on the main test route. So while not common (yet) battery-electric buses are around. More to the point, battery- and fuel cell-electric buses are the only ones that qualify as "electric buses" for the ARB mandate to go all electric, so there's a strong incentive for transit agencies to go that way. For the most part, they're replacing natural gas-powered buses, though SF stuck with diesel (hybrids) so the localized emission reductions from electric are probably more there than in LA, per mile driven.