Flying vs. driving
Posted by Yankee on October 2, 2005 - 11:25am
Disclaimer: I warn from the start that these are the proverbial back of the envelope calculations.
(And in especially tangentially-related news, British Airways has implemented a carbon offset program for their especially green-minded consumers.)
Then, I went to fueleconomy.gov and looked up the specs of our car, a 1994 Honda Civic Hatchback. I customized the settings to better reflect our habits: 6000 miles a year (actually, this is overkill), 70% highway driving, 30% city driving. This car gets about 35mpg on the highway, and has an annual greenhouse gas emission of 2.5 tons. For a trip of 1000 miles (NY to Raleigh, round trip), our car would emit roughly 336kg of CO2.
As for fuel consumption, this google answers article provides some numbers.
According to British Airways, a 747-400 plane cruises at 576 mph (927 km/h), burns 12,788 liters (3378 US gallons) of fuel per hour, and carries 409 passengers when full. If the plane is 75% full, one passenger is carried 22.2 km for each liter of fuel burned (52.2 miles for each US gallon of fuel burned). This fuel efficiency exceeds that of almost all cars, when the driver is travelling alone.*
So my roundtrip travel from NYC to Raleigh (if we were flying a 747, which is not usually true)** would require 19 gallons of fuel per passenger (38 gallons for the two of us), as compared to 28 gallons for the two of us to go from NYC to Raleigh in the car (1000 miles / 35mpg = ~28 gallons). So once you have 2 people in the car, it's worth it to drive from New York to Raleigh on the basis of fuel consumption and C02 emissions. (And not to mention cost, except that we had gotten frequent flier tickets.)
Which brings us inexorably back to the question: how does the fuel consumption and C02 emissions of the flight compare to the time (about 10 hours) and heartache required to drive from New York to Raleigh?
*It's not clear to me that the amount of oil used in jet fuel and gasoline are really equivalent. Is there as much crude oil per gallon of gasoline as there is per gallon of Jet A-1 jet fuel?
**I can't find the fuel consumption statistics for our Embraer 145. How would a 50-person plane compare to a large 747 on these specifications?
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Cheers,
Roy
I think driving is worse than flying, even if they do use similar amounts of oil. Driving requires a continuous stretch of tarmac, whereas flying only needs a few hundred yards at each end. And most of the pollution from flights is released into the stratosphere, not into towns at the head height of children. Flying is also safer, both for people in the plane and for innocent bystanders.
Nobody operates actual nuclear powered trains, though they are technically (if maybe not economically) feasible. France's solution probably makes more sense in any case.
this link covers it briefly, from the bbc
http://news.bbc.co.uk/1/hi/sci/tech/4266466.stm
I've not read the whole report but it looks like something I've been wanting to check out for a while. Thanks for starting the thread on this topic.
That would probably explain why general aviation is so bad. Small planes use a lot of energy to get just a few people up in their air. I guess. Haven't thought about it enough yet.
Here's another tidbit I came across. I'm clearly not vouching for the accuracy or authenticity of these references, but they seem reasonable so I'll then people can analyze. They might lead to other sources of data as well. Check out table 4 in this reference (link)
By 50mpg diesel car uses 8 (UK) gallons (36 litres)
By 35mpg petrol car uses 11.4 gallons (52 litres)
By 10mpg diesel coach uses 40 gallons (181 litres)
By 1.1mpg* diesel electric train uses 364 gallons (1653 litres)
By 0.76mpg** Airbus A321 uses 528 gallons (2400 litres)
* Based on 7kg of CO2 per km and compared to a 52mpg diesel car that produces 146g of CO2 per km.
** Based on 400 miles taking 48 minutes and fuel consumption of 660 gallons per hour.
If the cars have two people in them, the coach has 30, the train has 350 and the plane has 160 the fuel per passenger works out like this:
Petrol car 5.7 gallons per person
Diesel car 4 gallons per person
Plane 3.3 gallons per person
Coach 1.3 gallons per person
Train 1 gallon per person
The numbers are all very rough and just the result of a couple of minutes on google. Fuel use is only one part of the equation though. You should also look at how much energy when into the manufacture of the plane, train or car and what it's life is. I mean cars typically last 10-15 years where trains and planes last more like 30.
And this is not to mention the energy expended in ground transportation getting to and from the airport. That needs to be factored into airplane energy consumption also.
"The crux of the transportation energy problem is that there are just too many people doing too much travel. The development and improvements of the motorized modes of transportation have enticed people into traveling more. The increased travel (and increased population) in the 20th century not only canceled out the 5-fold gain in fuel efficiency but increased fuel consumption for travel 40 times. Thus, in addition to striving to increase fuel efficiency, it's even more important to strive to reduce the need for travel as well as to reduce population."
Bingo.
The "how often you do X" multiplier is just as important as the "how efficiently you can do X" factor, and it's often the easier of the two to improve by a given percentage.
This is why I've been saying for some time that one of the businesses that will boom like crazy in the coming years is anything that lets businesses substitute virtual meetings for real, in-person meetings with distant people. There are many solutions that do this already, of course, but my feeling (based on my years as a programmer, computer consultant, and technical writer and editor) is that it's still a new and immature technology.
The sticking point right now is probably the human factor. Adoption is always slow to spread. Part of it is just time; you need the old guard to move on so that the new guard can adopt these technologies.
The first time we ever met in person was more than a year after we started CRN.
"*It's not clear to me that the amount of oil used in jet fuel and gasoline are really equivalent. Is there as much crude oil per gallon of gasoline as there is per gallon of Jet A-1 jet fuel?"
You are right that they are not equivalent, but it isn't really possible to compare the amount of crude required to produce a unit of each. Both gasoline and kerosene (jet fuel) are natural fractions that occur in crude and are separated at the distillation stage through boiling.
Gasoline is among the lightest components of the barrel. It has 5-12 carbon atoms per molecule and boils off at 30-210 degrees centigrade. Kerosene is heavier than gas, but lighter than diesel. It has 11-13 carbon atoms per molecule and boils off at 150-250 degrees centigrade (UBS).
Based on average yields for US refineries n 2000, one barrel of oil yields 19.4 gallons of gasoline and 4.3 barrels of jet fuel (API). Actual production from a given refinery would vary based on its crude content and equipment. Converting kerosene to gasoline can be done using capital equipment (I believe catalytic and/or hydrocracking - but may be wrong). A heavier crude would produce more jet fuel and less gasoline. Refinery configurations are largely based on investment driven by demand or regulations.
However, for the purposes of your analysis, I think it is OK to ignore this and look at them as comparable.
The first thing that popped into my mind when I read this post was that the plane was going to make that trip from NYC to Raleigh whether or not you were on board. So if you want to minimize then obviously you should always fly and never add the extra emissions from the car to the "inevitable" plane emissions.
Trying to compare the emissions may be an interesting intellectual exercise, but in the short term it doesn't lead to any useful answers. Put another way, this is an illustration of just how difficult the greenhouse gases problem is.
-tedious john
We need to start letting the fossil fuel industries consolidate and start jacking up prices to consumers. They've been taking advantage of backrupcy laws to continue operating at ever lower costs. It's going to destroy the airline industry in the long term while it encourages overconsumption in the short term. Going back to a regulated system where the carriers are guarenteed to make a profit on each route might make sense - but it means prices will be much higher.
Subsidizing airports and highways need to end now.
I disagree - comparing emissions is much more than an "intellectual exercise". Understanding that driving creates less greenhouse emissions than flying is very useful info that allows people to choose how to have less of an impact.
It seems a misleading justification to say the plane will "make that trip ... whether or not you were no board," and to think that this means we should choose to fly instead of drive.
Every time you use any form of transportation, you increase demand. When you drive you increase the demand for gas, tires and roads. When you take public transit you increase the demand for transit (using less resources). When you fly from NYC to Raleigh you increase demand for that flight. If demand is high enough, some airline adds another flight. If demand is too low, they drop a flight (= less greenhouse gases, and we're closer to sustainability).
An unfortunate extension of this concept is the fallacy that, "if I conserve energy, someone else will use it anyway, so why conserve?" By using less energy (or any resource) you reduce demand, and you have less of an impact. The individual choices of millions of people do add up to make a big difference.
-- Steve
Long-term, sufficiently more individuals asking to fly will result in more flights, more fuel consumption, more emissions. It is a step function: the airlines need to be assured that they will, on average, exceeed their breakeven load factors. Being able to fill 2, or 5, or 10 additional seats won't cause a new flight to be added, though it depends on the size of the plane. Being able to fill a sizeable proportion of the seats on an extra flight probably will generate more planes and more emissions.
Short term, I'm with John here. I'd look at the one extra (marginal) passenger. If there is a seat available, you can fly in that seat and produce essentially no incremental C02. If you want a seat, and they don't have one, they won't add a plane for you today. But if you drive instead, you produce lots of extra C02. It is a real increase in C02, attributable directly to your choice.
There may be a personal strategy to use here. Planes flying at off-hours, early or late, are less full. Some can be almost empty, and will be flown regardless, because the airline needs to shuttle the aircraft to another location. If you choose to fly on emptier flights (which also have the cheapest fares available) instead of driving, you may be doing the environment a favour.
But the best choice remains staying put.
Every day there are thousands of flights, and thousands of people deciding whether they should fly or drive. When enough choose not to fly, there's one less plane flying. Now think of all the people who are no longer flying on that plane, every time it doesn't fly. Your choice not to fly may tip the balance so there's one less plane - think of all the CO2 you've saved, every time that plane doesn't fly!
These things average out. If you can't stay home, choose to drive and tip the balance toward one less plane in the sky.
A 747 is a fairly old design, and I was reading somewhere that by modern standards it is considered a fuel hog.
Then again, the airlines that have them probably have them mostly paid off by now (or they purchased them a long time ago when costs were much less), so the airlines keep flying them because they can still make it pay.
The recent battles between Airbus and Boing are interesting. Airbus is building a behemoth to take the place of the 747, but it isn't clear to me that there is a market for such a plane in the world we are entering. The Boing 7E7 seems like a better bet, but then again in the long term it may be that neither one is going to be viable.
Now of course everybody will yell that that scheme is way " too expensive". But, if that is true how come we read about these things all the time in science fiction stories???
And also, just what fraction of the true costs are we counting?
In particular look at Chapter 2, figure 2.11
Here's most of the data from that table:
Energy Intensity of various modes of passenger travel (2002)
Persons/vehicle BTU/mile BTU/psgr/mile
Auto 1.57 5623 3581
Light Truck 1.72 6978 4057
Motorcycle 1.22 2502 2274
Demand-
Response 1.1 14449 13642 (e.g. svcs for senior citizens and disabled)
Vanpool 6.3 8568 1362
Buses
Transit 9.1 37492 4127
Intercity 932
Air
Commercial 95.8 354631 3703
Gen Aviation 10384
Rail
Intercity 14.0 67810 4830
Transit 22.1 72287 3268
Commuter 33.5 90845 2714
Somewhere else in the report is this data:
Energy intensity(Btu/ton-mile) United States, 2002
Trucks 3,476
Waterborne commerce 471
Class 1 railroads 345
45% of 42 gallons is 18.9, which was at least a Civic-worth the last time I filled one. It's about half a gallon more than I've ever gotten into my Passat.
jmscaptain is right about the portions of product produced in the first stage of refining, however, he wrongly called it cracking. This stage is distillation, which mereky separates naturally occurring components of crude. Cracking is a later, more advanced stage that actually converts molecules of one distillation product into a lighter, more valuable one.
As the US refining sector is highly complex (ie. sophisticated/capital intense), it does convert a significant portion of heavy distillation outputs into lighter products such as gasoline, hence the final output of 45% gasoline in the EIA data the EP linked to.
Refining (cracking in particular) is volume expanding. 42 gallons of crude input come out as slightly more than 42 gallons of product output. According to API the average refinery in 2000 produced 44.6 barrels of product from 42 barrels of crude, an addition of 6. So on average, it can be estimated that a gallon of crude input yields a little more than .45 of a gallon of gasoline in the average US refinery. So it would take less than 20 gallons of crude to fill ianqui's tank. The same crude input would also yield 5 gallons of diesel, 2 gallons of jet fuel, some fuel oil, LPG and other products.
During takeoff, the maximum fuel consumpton of the A319 is about 12,000 pounds per hour for each side. So that's a max of 24,000 pounds per hour for the whole plane. He said 20,000 pounds per hour would be about typical during takeoff.
At cruise, he said consumption would be about 6,000 pounds per hour, including both sides of the airplane. During descent, almost nothing -- descent is basically a glide. Then there will be some usage during the runway approach, but I don't have information on that part. It takes place at lower altitudes but at slower speeds, so I'm guessing it would be similar in fuel consumption to cruising at altitude.
I asked Calchemy, the Palm units-conversion calculator, how many gallons per minute is 24,000 pounds of kerosene per hour, thus:
(24000 lb/hr) / d_kerosene ? gallon/minute
and it answered
58.523238 gallon/min
which is almost a gallon of kerosene per second. Or, if you like, about four average-size automobile fuel tanks per minute.
So if you have ever wondered how those jetliners manage to get up into the air, here is your answer: enormous kerosene fires, spewing out hot gases, under each wing.
Another interesting point: at maximum takeoff power, the A319 would use up a typical load of fuel (about 23,000 lb) in about one hour.
Finally, I'd like to point out that liquid fuels enabled the invention of both practical automobiles and any kind of airplane. Supposedly Mr. Diesel originally designed his engine to run on powdered coal. Imagine flying over the ocean on powdered coal, and you will appreciate just how important liquid fuels turned out to be.
If Leonardo had had access to crude oil and some advanced metallurgy, who knows when humans might have started flying?
That simple conclusion may be obvious to most people here, but it shocked me as I was sitting there, half asleep at around 24,000 ft, on my way back to Philadelphia. I thought, why are we spending so much time on alternate fuels and war for oil and so forth? We should be working on reducing friction.
Lo and behold, on this thread, what is the most efficient means of transport? The train, where, because of the smooth rails, friction is much lower than for any other type of vehicle.
Think low friction!
Additionally, although a physics teacher might say you are "recapturing" the climb energy on descent (by converting mgh potential energy into 1/2mv^2 kinetic energy), when the plane brakes on landing, you convert that kinetic energy into waste heat energy. So you are not recapturing anything. If the pilot uses reverse thrust to slow the plane, you are actually burning more fuel to counter the effects of the "recaptured" energy.
(P.S. Trains do not have elastic rubber tires and thus do not lose energy to wheel flection. You do want large friction between wheel and rail so that your wheel can grip the road, so to speak.)
(p.p.s. Some more railroad physics trivia:
http://www.spikesys.com/Trains/whel_faq.html
http://www.spikesys.com/Trains/ )
Thus, far less fuel is expended per horizontal mile of flight during the glide phase than in the climb phase. In fact a plane could shut its engines off and still glide for a goodly distance before it landed (or perhaps more accurately, crashed). However, the higher the wing loading, the shorter and steeper the glide path, which is why high-speed jet planes make for poor gliders.
However, not all of this potential energy is recovered. As you correctly pointed out, when the plane lands, it still has a considerable amount of kinetic energy left that must be disippated through deliberate air drag my means of flaps and by the braking of the landing gear.
On a lark, I checked out round trip tickets from San Diego to New York City on the following:
Honda Insight: 2800 miles each way, $330 gas for round trip, 43 hours transit each way
Greyhound: $289 with approx. 68 hours transit each way
Amtrak: $360 with approx. 60 hours transit each way
American Airlines: $280, 5 hours transit each way
For the Honda Insight, I assumed 55 mpg and a gas price of $3.25/gallon. Note that costs above are for round trip tickets (or gas for the Insight).
So in summary:
Mode Cost (round) Time (one way)
Car $330 50 hrs
Bus $290 68 hrs
Rail $360 60 hrs
Air $280 5 hrs
And this does not even include the cost of food for Car/Bus/Rail nor the need for two drivers in the case of Car or lodging or several lines of methamphetamine.
I suspect the additional ten hours of or twenty hours between bus and train and car is the need for loading and unloading passengers at stops along the way, as well as change of bus.
Another little quibble. Folks, are we really doing the right thing by comparing costs here in the good ol' USA, when we all know how much better other people around the world do things, like trains in Europe? We all probably have experienced the luxury of knowing exactly when our train was going to leave, and exactly when it was going to pull up to the platform in Stuttgart, or whereever.
So maybe we should be doing the harder thing- comparing true costs (like including asthma, war deaths and all that) of the best way we could do things, not the dumb ways we are doing them now and the totally nutty if not immoral ways we figure costs.
Given the current nature or our transportation technology in all forms, it would make sense that getting a body from point A to point B is not going to vary tremendously in terms of energy use depending on the mode. (However, first lifting that body several thousand feet into the air would seem to add considerably to the energy needed to get from point A to B.)
Then, it occurred to me that what we might need to compare is time. If I get to Seattle in four hours, vs. driving in two days, then I have an awful lot of time to use up other high energy consumption modes of travel, including flying to other places during those two days.
Maybe we need a new index of energy consumption: PER HOUR PER PERSON.
In answer to someone's comment about train travel being used by those afraid of flight, I don't agree. I find rail travel to be very relaxing and even poetic. You travel through country that is oftentimes fairly pristine compared to highways. There is a rhythmic sound to the train, and oftentimes an interesting commeraderie between travellers. Unfortunately, there is no good route between Seattle and Colorado.
Last thought, if we really want to talk efficiency and ecology, the best answer is bicycles. But the U.S. is so huge, this is oftentimes very impractical.