The future of cars includes diesel, electric, and—maybe!—fuel cells

September 29, 2015, 6:34 PM UTC

The United States should be laser-focused on getting the gas mileage of every car to reach 180 miles per gallon.

That’s according to Margo Oge, the former director of the Office of Transportation and Air Quality for the U.S. Environmental Protection Agency and the author of Driving the Future. Speaking at Fortune’s Brainstorm E conference on Tuesday in Austin, Texas, Oge added that the nation should also be focused on ensuring that each one of those highly efficient vehicles is powered by renewable energy sources.

One problem, though: The pace of vehicular electrification has been slow, said Jerome Guillen, the former vice president for worldwide sales and service at Tesla Motors. “Electric is slower than we had anticipated.”

Tesla (TSLA), of course, is known for pushing the envelope when it comes to electric powertrains and is preparing for the official launch its Model X sport-utility vehicle, scheduled for later today in California. Even with Tesla delivering about 50,000 cars this year in a market of 17 million new vehicles—a “drop in the bucket,” but one worth being proud of, Guillen said—progress must be much faster, on many levels, to achieve Oge’s dream.

And in the meantime, what about other energy sources? Oge thought diesel technology could still be a viable alternative despite the emissions scandal that has enveloped Volkswagen. Volkswagen vehicles are believed to have emitted up to almost 1 million more tons of pollutants into the air than expected.

Stefan Knupfer, a director at McKinsey and Company, was also optimistic. “I believe it’s too early to say goodbye to diesel,” he said. “We will see more and more electrification, …but there will be a transition period and some kind of combustion will be needed. And if diesel is not as good as we thought it would be, then we will need another kind of technology.”

Fuel cells aren’t it, though. “Someone referred to them as ‘fool’s cells,’ I believe,” Guillen quipped.

Whatever the case, the trajectory is clear: The automobile is poised to become radically different than what we know today, from how it’s powered, to how it’s controlled, to even how it’s owned. Here’s to the fast lane.

Click here for more coverage of Fortune’s Brainstorm E conference.

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