General Motors' venture capital arm GM Ventures has invested for the second time in Proterra Inc, an electric bus maker.

The Greenville, South Carolina company makes the EcoRide, a battery-electric bus that achieves the equivalent of 24 mpg in a diesel-engined bus.

Proterra's EcoRide can also be fast-charged in only ten minutes, and has a range of 40 miles.

The Detroit News confirms that GM Ventures and six other companies have invested a total of $23 million into Proterra, which will go towards increasing delivery of the EcoRide to new customers and markets. Proterra now has seven transit authority customers, up from two in the last 18 months.

GM previously invested $6 million into Proterra Inc, back in June 2011.

The company says it wishes to identify and invest in technology solutions which help advance the global transportation industry.

John Lauckner, president of GM Ventures, said in 2011, "While this investment will help Proterra commercialize its electric bus and fast-charging technology, it also helps to address the future challenges of urban mobility."

Proterra says the EcoRide bus, powered by 54-72 kWh lithium-titanate battery packs, can easily replace up to 80 percent of diesel buses in typical transit and shuttle routes, without altering schedules or passenger service.

Electric buses are already popular in other parts of the world--the cities of Genoa and Turin in Italy have been using electric buses for over a decade.

For GM Ventures, Proterra is just one in a series of companies the venture capital firm is investing in. The company is also putting capital into battery and electric motor technology, connected vehicle tech, advanced materials, and more.

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