"there was an interesting piece in the New Yorker a couple of years ago, pointing out that RMI is an environmental disaster compared to a couple in a 1 bedroom flat in Manhattan, in terms of energy consumption.  The difference being the cars and the amount of living space."

Do you have a link?  It would seem a little unfair to compare a commercial business building with something like 40 employees to a residence of 2 people.  I doubt, even with the extra space, that a Manhattan flat could even come close to matching the RMI in terms of fossil energy used...the RMI doesn't even have a heating system, it relies on passive solar and the heat generated by the occupants and computers/lights/etc inside.  Now the cars thing...that you could get them on.

I think it was on a per person basis.

The key was the driving (or lack thereof).

Unfortunately the New Yorker archive is not online in any form that I can find.