Flight of Fancy - A plane better than a Prius?

The Guardian is reporting that engineers have designed a 'flying wing' called the SAX-40 which would achieve 149 passenger miles per gallon compared with 121 for a Boeing 777. A Toyota Prius hybrid car (or a good diesel) gets 144 passenger miles per gallon. I don't know over what distance they make the comparison as obviously an aircraft has to go up and down as well as across, if you know what I mean.

This won't save the planet on its own, but it would be significant progress. If I could magic up one techno-fix, I think an even better 'plane than this would be it...