Tesla used to do something similar in its early days (with Toyota, Daimler and others), but gave up most of these projects as it moved toward focusing solely on vertical integration and making its own vehicles. Fittingly, the new Proterra business line is led by Tesla alum Toby Kraus (many Proterra employees come by way of Tesla, including Proterra CEO Ryan Popple).

Kraus tells us in an interview that in order to make the best electric transit bus on the market, the company had to invest significantly in technology around battery packs, drive systems, charging systems and software.

That tech development can cross over in applications for other types of heavy duty vehicles, such as garbage trucks, urban delivery vehicles, school buses and shuttle buses.

Proterra's news is an interesting development and highlights a few important trends across the electrification of transportation:

• Urban commercial vehicles are prime to electrify as the costs of batteries drop, as states such as California offer mandates and incentives, and as companies and public agencies strive to hit sustainability goals. The Proterra folks are eyeing commercial vehicles that are "high mileage and inefficient," as Kraus put it.
• Most large OEMs that make the world's commercial vehicles aren't being particularly aggressive on launching their own EV trucks. If they don't have the technical chops, a third party could be an attractive partner (or perhaps maybe they'd want to someday buy Proterra outright). A lot of the electric commercial vehicles available right now are from startups.
• Building out charging infrastructure for electric commercial truck and bus fleets is a complicated business, and Proterra, as do many others, provides coordination on the grid level. The fact that Proterra already has substantial experience with this via the transit bus market gives it a leg up. Infrastructure continues to be one of the biggest barriers to widespread adoption of commercial electric fleets. 
• Proterra, despite its pioneering transit bus line, has long been constrained by manufacturing. The company is reportedly eyeing an IPO, and it's always good to get as much revenue as possible on the books when both bus sales cycles and deliveries tend to take time. 

For years, Proterra's Ryan Popple has described the electric transit bus market as the tip of the spear in the electrification of commercial vehicles.

Popple will be speaking on such topics, but also on leadership in the clean economy, with former Michigan Gov. Jennifer Granholm at our VERGE 19 conference in Oakland in October. Come on out.