"We really and truly expect that fuel cells are going to double the fuel efficiency of the best internal combustion engines and in some cases triple it, " Roan said.

CNN: Bus showcases fuel cell technology

Now, it's true that amazing gains are being made in the efficiency of internal combustion engines, both gas and diesel: direct injection, cylinder deactivation, stop-start, eco-mode throttle mapping, to name a few of the recent applied technologies.

WSJ: Ford C-Max Hybrid Energi: The Bawdy Electric

The key to thermal efficiency for internal combustion engines is compression ratio.

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