Okay, since i don't have the specific fuel consumption figures for the A319 I'm going to attempt a rather crude estimation here. It's crude for two reasons. Firstly, not all engines burn 'as cleanly'...ie, the burn the same amount of fuel but some burn more completely so they produce less Nox and Sox. (however CO2 should be similar?)
Secondly, the MTOW for aircraft varies and its fuel capacity might not be the restricting factor to an aircraft's range (ie - same fuel capacity on A320 and A319 different ranges may be more restricted by weight carried rather then by fuel...once again not sure, any pilots type rated here wish to comment?)
The A320 series has a basic fuel capacity of about 23860 L. At A 64 ton Max takeoff weight, the A319 as a range of around 3350 kms. (basic A320 range of 4800 kms for same fuel capacity!!!!! take note!) Lets do the VERY crude thing and divide 23860/ 4000km (to try and estimate actual fuel consumption, as at MTOW(full load of passengers cargo in high density arrangement) the a319 is going to be fuel restricted and its fuel consumption will look higher then what it actually is - that is, it isn't going to use full tanks to achieve its max range of 3350 kms...needs the option of more powerful engines selected in order to use full tanks)
Now lets assume a typical LCC configuration of 144 seats. (typical of UK flights these days, and less efficient then easyjet's 156)
So we take of Fuel and divide by 4000 kms and we get a 5.956 L per km usage . (which obviously is an average of the much higher consumption for takeoff and then cruise)
According to Mappoint, the distance from London to Edinburgh is 639.2 kms (CBD to CBD). And, LHR
on the great circle mapper is 533kms (remember planes can fly a more direct path, Car's must stick to the highway)
So, our Airbus A319 carrying 144 passengers burns 3179.3 L of fuel. Or, just 22.08 L of fuel per passenger!!!!!!! quite stunning really. In reality it would be a bit higher due to holding patterns etc. Lets Assume 4500 litres to be on the safe side, allowing for holding patterns, full takeoff power settings to be used
Now lets take our 100 cars going to Edinburgh. lets assume an average of 10L of fuel per 100 kms travelled. (allowing for both old and new cars, big and small to be used, plus one can't travel at the ideal rate because the road has places where one is forced to stop or slow down, going thru small towns etc) 100 cars is a safe estimate because many people travel alone in their own car or with just 1 other person, unlike airplanes who generally are forced to fill or near fill their planes in order to be commercially viable. So each car then uses 63.92 L of fuel for the same trip, wich by 100 becomes 6392 L of fuel used.
So here we have it. We have an estimated fuel consumption for the A319 at 3179 L, but allowing for 4500L to be on the safe side, and 6392 L of fuel to be used by the 100 cars. The Airbus is clearly more environmentally friendly if the cars are used in this manner (and they typically are)
So go tell that to the anti-flying ppl.