What’s the right ratio of public charging stations to plug-in electric cars sold?

2018 Kia Niro Plug-In Hybrid charging at ChargePoint station, Santa Cruz, California, Dec 2017Electric vehicles still make up just a tiny slice of the vehicles on the road across the United States. Still, with impending regulations and more longer-range electric vehicles soon to arrive, governments far and wide recognize the need to encourage the installation and growth of public charging stations. Just how many charging stations is enough...