Strepsils:
Because all other things being equal we have to account for the fact that air transport can take more direct routes from A to B and is hence more efficient in this regard. As Old Smokey says, this makes for a fairer comparison.
Personally, I would dispute the x1.5 figure. If a car followed a zig zag route making 90 degree turns once in a while whilst an aircraft went in a straight line the car would do sqrt(2) more distance than the aircraft - another 40% or so. I would say therefore that a figure more like x1.1-1.3 would be more appropriate.
It doesn't feel like I'm going to most direct route from the Canaries to Newcastle, however, when we come off the Tango routes and go WAL-POL-NEW!
