Cars vs planes
416 wordsBefore I start, apologies for my egregious use of non-metric measures in this post. This is because all the sources I’ve used provide Imperial values. I tried starting by converting to metric, but I botched it, and started again the lazy way.
Further to my last blog entry, I’ve seen quite a few articles in papers recently suggesting “green” holidays travelling to the same destinations by land transit, because flying is so expensive in terms of CO2 emissions.
I thought it might be interesting to find out what the figures were, so I Googled for it. I didn’t find anywhere with at-a-glance CO2 per passenger mile comparisoms.
Then in today’s Guardian, an article about a clever new plane design contained some figures:
- clever new plane: 149 passenger miles per gallon
- Boeing 777: 121 passenger miles per gallon
- Toyota Prius hybrid car: 144 passenger miles per gallon
This was much closer than I’d expected; I could only guess at what the occupancy of the Prius was. Why was air travel being demonised so? Of course, I thought, burning aviation fuel must release more CO2 per gallon than burning car petrol. So I picked a likely looking web site to find out: The Cool It Campaign’s “method” page.
It turns out that aviation fuel releases marginally more CO2 than petrol: 21.095 vs 19.564 lbs/gallon.
Armed with this knowledge, I set about working out the CO2 impact of driving versus flying.
| Constants | Calculated | |||
| Fuel pm/gal | CO2 lbs/gal | Fuel gal/pm | CO2 lbs/pm | |
| Car occupancy 1 | 22.400 | 19.564 | 0.045 | 0.873 |
| Car occupancy 2 | 44.800 | 19.564 | 0.022 | 0.437 |
| Car occupancy 4 | 89.600 | 19.564 | 0.011 | 0.218 |
| Plane | 40.860 | 21.095 | 0.024 | 0.516 |
(”pm” is passenger mile)If anyone can point me at the fuel economy and CO2 output of buses, trains and passenger ferries, I’d be interested to know.
The conclusion appears to be that to travel the same distance, flying gererates less CO2 per passenger than a car with only one occupant. If there are two people in the car, it’s really quite a close thing, but bear in mind that planes can travel in straight lines whereas cars have to follow roads. If you drove from London to Cairo, you’d probably rack up more miles in your car than you’d have flown. If you get more people in the car, you’re greener than a flier.
Also bear in mind that the constants are US figures. European cars might well guzzle less fuel on average.
But of course, my last post was mostly in favour of travel. I still think people should see the world, and most of us don’t have enough time off work to get to exotic places any way other than in a plane.
November 10th, 2006 at 17:20
That’s a thought-provoking post.
I’m not sure that the Prius or the Boeing are indicative of the average car or plane, which might be where there’s a discrepancy.
I found the following related links:
http://ask.metafilter.com/mefi/25722
http://answers.google.com/answers/threadview?id=48121
They suggest wildly different passenger miles per gallon, depending on the plane. The Boeing probably isn’t typical. That said, those links broadly support the idea that plane travel is more efficient than car travel. Certainly, if I’m that high up in the air, I know which I’d rather be inside.
I think the key thing is that even if a plane is more efficient than car for long journeys, the sheer length of the journeys involved carries a massive environmental burden. It’s the rapid increase in journeys taken, fuelled by cheap and virtually free fares, that is the problem. Whereas people used to take two flights a year, people now routinely take ten or twenty. The way to cut emissions isn’t to make planes more effective, but to stop taking so many flights.
I feel conflicted on this - I love travel, and planes are the only way to feasibly get to many places. But if I can start by taking two fewer flights per year, that’s a massive saving I can personally make in CO2 emissions.
On this theme, I strongly recommend everybody watches Al Gore’s film ‘an inconvenient truth’. It’s very scary but also inspiring.
November 10th, 2006 at 23:50
We don’t decide how much carbon is burnt by planes or cars, OPEC decides that when they sit down and decide how much to produce in any given time. You see, when they decide a production rate, out it comes from the ground and it all gets burnt, excluding a small percentage used for lubrication. If they simply decided to reduce the outputs, everyones so called carbon footprint would go down. market forces would see to that.
Seems too simple though don’t it?
November 13th, 2006 at 13:09
JC: that’s very thought provoking. I’m not enough of an economist to speculate at the market forces which affect OPEC’s machinations though.
Sean: True enough. A Prius is meant to be especially fuel-efficient, while I consider a 777 as being the standard plane for a long haul journey — the vast majority of my own long haul flights have been in 777s.
But, the figures used for those tables are not Prius/777 figures. Check the source page for the real deal, but from memory, the car figure is the distance travelled by American cars divided by the amount of petrol sold in the US in the same period, and the plane figure is the distance travelled by US passengers divided by the jet fuel used in the same period.
Especially in the case of the plane figure, it looks like a useful number taking into account underbooked flights etc.
November 13th, 2006 at 14:01
[...] I’ve done some further digging since my last post about the CO2 impact of cars and planes. [...]