General Motors (GM) has gotten lots of buzz for its Chevy Volt, but the automaker’s most important electric vehicle contribution may not have anything to do with autos at all.

GM today announced a partnership with Proterra Inc., a Golden, Colo.-based maker of “zero-emission commercial transit solutions.” More specifically, Proterra makes fast-charge electric buses and automated bus charging station (10 minute recharges). Its initial vehicles were rolled out to Pomona, Calif. last September, and both San Antonio and Tallahassee have signed up for later this year.

This could be welcome news for anyone in those communities who lives or works near a major bus depot, or for bus riders who get blasted by gray clouds when waiting for the right route to stop by. It also could represent a pollution paradigm shift in certain emerging markets, where urban buses are an even more vital mode of transport than here in the U.S.

GM’s initial involvement with Proterra is financial. Its venture capital arm, GM Ventures, today announced its participation in a $30 million funding round led by Kleiner Perkins Caufield & Byers. Other backers include Mitsui & Co., Ltd., Vision Ridge Partners and 88 Green Ventures. Prior to this, Proterra raised $20 million from MK Energy and Infrastructure.

There is no commercial agreement between GM and Proterra, but you certainly could imagine one down the road. GM does not currently manufacture any municipal buses, so Proterra’s version could ultimately serve as a foray into that market (expectations are that Proterra costs will soon become competitive with diesel-hybrids).

For Proterra, the GM investment means validation and access to research. “A good example of how we can [leverage the relationship] relates to energy storage systems,” says Jeff Granato, president of Proterra.