It depends on what on what you mean by “ecofriendliness”. In my thermal energy conversion class the professor came to the conclusion that since a gas turbine is less efficient than a piston engine a car is more efficient and “ecofriendlier”. But what about the friction, the CO2 produced and all those other factors? There are various metrics for measuring ”ecofriendliness” but I think this is the most apropiate: equivalent warming potential (in CO2e)/[# of people transported * distance (in miles)] . I didn’t include speed so guess which one produces less global warming potential? The official global warming potential is explained here. A simpler but adequate explanation without integrals is here.
Here are the calculations:
Average number of people per car (in the US): 1.3 people
From: http://journeytoforever.org/biodiesel_404.html
Warming potential of average US car per mile: 1.192 CO2e lbs/mile
From: http://www.google.org/recharge/dashboard/calculator
“Ecofriendliness” of car: 1.192/1.3 = 0.917 CO2e lbs/mile
Warming potential of Boeing 747 per passenger in a 5177 km trip with 100% occupancy: 1815 CO2e kg
From: http://www.chooseclimate.org/flying/mf.html
“Ecofriendliness” of airplane: (1815/5177)*(0.62137)*(2.20462) = 0.480 CO2e lbs/mile
So airplanes carry more people faster and produce less greenhouse gases (based on the data).
