The world's largest car market is on track to convert bus fleets to battery electric, a transition fueled by aggressive government subsidies and mandates. According to Interact Analysis, 80,000 electric buses were delivered globally in 2018 -- and 99 percent of those were in China. Some cities, like Shenzhen, have already gone entirely electric. "If you look at the impact that that's had on China, they have reduced their daily oil consumption by over 200,000 barrels" says Ryan Popple, CEO of American electric bus manufacturer, Proterra.

In the US, however, the adoption of electric buses is happening at a much slower pace. Out of all the electric buses delivered last year, the US accounted for just 300. But that is starting to change. North of Los Angeles, Antelope Valley Transit Authority is close to becoming the first all-electric metro fleet in the US. And places like New York City and California have set goals to gradually transition to 100 percent zero-emission bus fleets by 2040.

Watch the video to learn more as CNBC explores why the US trails China in electric buses.