For those commenting on power sources - yes, to achieve fully emission-free transportation, utilities & markets need to move towards clean energy supply (both on- and off-grid). The buses from Proterra are a step in exactly the right direction. You need advancements in new technologies and clean energy supply to get to a 100% clean energy future.

Some places are already well set up for a grid-supplied clean electric transportation system, like my hometown Juneau, Alaska. Cleantechnica shout-out here: https://cleantechnica.com/2015/10/22/embracing-clean-electric-transportation-in-juneau-alaska/

Thanks for the coverage Andrew Beebe!