That's 14,000 electric buses. In just one city.

I'm a big believer in the importance of sending a signal. So when 12 major cities committed to only buying electric buses from 2025 onwards, I was impressed. After all, it sends a powerful signal to investors and vehicle manufacturers about which way the market is ultimately headed.

I was impressed, that is, until I read over at Cleantechnica how Shenzhen—a city of 11.9 million residents in the Guangdong province of China—will have entirely electrified its bus fleet of more than 14,000 vehicles by the end of 2017.

Now that's what I call really sending a signal to the markets.

Of course, Shenzhen has a home field advantage because it happens to be home of BYD, a leader in the field of electric vehicles, in general, and electric buses in particular. And China has been streets ahead of other countries in terms of electric bus sales. Nevertheless, switching over such a massive fleet in the space of a few years (Cleantechnica reports the transition began in 2011) is an incredible achievement that ought to drive higher ambitions from the rest of us.

Worth noting, of course, is that while electric vehicles are likely always greener than gas or diesel vehicles of a similar size, the full green benefits of Shenzhen's transition will only be realized once the grid they run on is significantly greener too. That said, buses and other diesel engines are a major source of smog forming emissions. Smog forming emissions are significantly impacting the output of Chinese solar. So switching to electric buses could actually increase the amount of renewables that are available to run those very same buses.