I think that even with an inefficient engine it would still use less fuel than a car that is fuel efficient to move a person short distances. So, in that case, it still seems better than a single occupant vehicle.

However, I would rather have a Stokemonkey when and if I ever get a cargo bike. Then I could comfortably peddle when I wanted to while being able to have assistance when I needed it. Some people even use them on regular bikes due to mobility issues. A friend of ours, Gypsie, had hers mounted to a recumbent that she used during her rehibilatation from an accident to help her up the hills around her home. After her recovery she moved it to an Xtracyle to help her haul her DS and cargo. She and her DH are car-free. Anyhow, her DH has one mounted to a Bakfiets and he helped to push me up a couple of the steeper hills near their home(West Seattle) after a cargo bike ride. I was totally surprised how powerful it was. I'm a total hill wimp even when I'm not trying to pull our child trailer(~30lbs) with DD(~30lbs) in it. But boy, did it ever feel like I was trying to pull a boulder at the end of that day! I could definitely feel the difference from when he had his hand on the trailer and when he took it off. BTW, he had his DS and my DS in the Bakfiets box:


The Stokemonke is the red cylindrical thing behind the box:

More pics of the cargo bike ride:
http://alexandchristine.smugmug.com/...9977#191584882