At the start of 2014, there were over 400,000 plug-in electric vehicles on roads worldwide.

That's according to an analysis by Zentrums für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW) in Germany.

As ZSW claims, this 400,000-unit figure represents a doubling from 2013 and a quadrupling from the start of 2012 when only 100,000 were on the roads.

Officially, ZSW pegs the number of plug-in electric vehicles on roads at 405,000 in the beginning of this year.

When will we crest 1 million?  According to ZSW, that will happen in early 2016.  The race to 1 million is on.

It's worth pointing out that none of the figures provided by ZSW included plug-in electric motorcycles, trucks or buses.

Plug-In Electric Vehicle Sales Chart - Automaker Breakdown

Plug-In Electric Vehicle Sales Chart - Automaker Breakdown