One of us is misreading the critique (and it may be me?).
I think that what it's saying is this:
* The most wasteful car trips are solo local commutes. Carbon-per-inch, flying is more efficient than driving when the driving is a solo local commutes.
* For longer trips, in a light duty vehicle like a sedan or SUV, driving usually smashes flying. If you have 4 people in the car, even in an inefficient car, you are using less than half the fuel of those same people flying.
The Michigan study simply averaged these together, which is obviously senseless because there is no flight equivalent of a 3-mile commute. It only makes sense to compare flights against highway mileage, and it's not unfair to assume >= 2.2 people in the car.
I think that what it's saying is this:
* The most wasteful car trips are solo local commutes. Carbon-per-inch, flying is more efficient than driving when the driving is a solo local commutes.
* For longer trips, in a light duty vehicle like a sedan or SUV, driving usually smashes flying. If you have 4 people in the car, even in an inefficient car, you are using less than half the fuel of those same people flying.
The Michigan study simply averaged these together, which is obviously senseless because there is no flight equivalent of a 3-mile commute. It only makes sense to compare flights against highway mileage, and it's not unfair to assume >= 2.2 people in the car.
That's the way I read the critique.