Flying vs. driving

When I was in North Carolina a couple of weeks ago, people asked me if we had driven or flown. Well, we flew. Coming from New York, the maximum driving distance for a weekend trip for me is about 4 hours. I'll go to Boston or Washington, but that's it. I think we all know that planes are less efficient than cars, but I wasn't sure how much, so I crunched the numbers for two factors: CO2 emissions, and fuel consumption.

Disclaimer: I warn from the start that these are the proverbial back of the envelope calculations.

I found a neato, if user-unfriendly, calculator on the web that tells you the greenhouse gas emissions that are produced per passenger on a 747 flight. I put in the coordinates for New York to Raleigh, NC, and it reported that for a round-trip flight, 713kg of carbon dioxide is emitted. There were 2 of us, for a total of 1426kg of CO2. (Although greenhouse gas emissions are more than CO2, it appears that both websites are basically reporting only C02.)

(And in especially tangentially-related news, British Airways has implemented a carbon offset program for their especially green-minded consumers.)

Then, I went to 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?

The correct answer is to take the bus. I have hopes that intercity bus service can become quite comfortable and much more appealing than either driving or running the airport/flight/airport security gauntlets. ....But that's just a dream.


Trains are even better, because they don't necessarilly use fossil fuels at all. The French TGV, for example, is largely nuclear-powered. (This may or may not be good for the environment, but it certainly helps reduce oil depletion and CO2 emissions.)

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.

Releasing pollutants directly into the stratosphere IS one of the major problems of flying. It is generally not considered an advantage.
If the concern is global warming, driving is generally better than flying, particularly with 2 or more passengers.  The roads are already there, and will continue to be maintained for decades to come.  Flying is just one of the many luxuries we have to cut back on (or give up) to reduce global warming and to lead more sustainable lives.
More correctly, the TGV is electrically powered, and since most electricity in France is generated by nuclear energy, it is true that France's trains are contributing very little to CO2 emissions or to oil depletion.

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.

It was recently in the news (21st sep) here in uk, that we would not meet our co2 emissions targets because airlines had not been factored in.

this link covers it briefly, from the bbc

Here's some info I found at IEA on energy efficiency and the transporation sector (link) and in particular take a look at figure 5.15 (link).

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.

Huh. In Fig 5.15, what do you think is the difference between "general aviation" and "air carrier"? I assume one is cargo?
General aviation is the umbrella term for non-airline, non-large-cargo aviation.  Weekend pilots, guys running one or two plane charter services, etc.  Some cargo falls into this category, but all the people you've ever heard of (FedEx, UPS, DHL, BAX, etc) don't.
Yeah, that one confused me as well.  What I've gathered so far is that "general aviation" includes small planes (e.g. two seaters, four seaters) whereas "air carrier" includes large jets.  I've seen some references to "general aviation aiports" which seem to be the small ones in our backyards compared to "air carrier airports" which are the large ones associated with each city (or a couple at most).

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)

Here are some back of the envelope calculations I did for fuel consumption, from London to Edinburgh is 400 miles.

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.

How may direct flights are out there? Delta gives me guest visit o atlanta whenever i trvel in the midwest. Cars have straight line advantage always.

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.
Here's a discussion of transportation and efficiency.  (link) His conclusion at the end is dead on:

"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 is right, TRE.

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.  

It's getting to the point where meeting in person is more about inertia than about necessity. We're no longer waiting for a silver bullet; the technology is already there in several different ways. Email, IM, teleconferencing, videoconferencing, video streaming, secure network traffic, and so on. Most of these technologies are pretty darn mature. You can't get by without EVER flying around, because face time is important, but companies can reduce the frequency. And they are doing so -- but slowly.

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.

I agree with this. I co-founded a non-profit that's been pretty successful ( given its small size and funding. I met my co-founder online when he wrote me about a paper I'd written.

The first time we ever met in person was more than a year after we started CRN.

Ianqui, you ask:

"*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.

These guys have done some analysis on the topic and are peak oil aware (link). Cool stuff here.

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

John, this is a tedious point, but, if half the people in the country decided that plane travel wasnt cool, was too expensive, or bad for the environment, those planes would not 'fly anyways' due to lack of demand. In fact, many global airlines are already on teh brink of bankruptcy and many non-US carriers are getting subsidized by govts.
OUr decisions do make a difference, if not in the moment then certainly over time they do. I used to travel a lot for business and I think there is an unwritten policy at many airlines to combine two flights if they are close enough in time. For instance I was traveling from Chicago to NYC on American last year and there was just 25 of us waiting for the 2pm flight - they just combined us with the 3pm flight and the flight was 5-10 folks short of being full. So if there had been just an extra 10 people there would have been a whole extra flight.

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
Which is why carbons taxes et cetera are an important step to take.
Both sides of this discussion are correct, depending on the timeframe you use.

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.

I still disagree.  Driving generally has greater impact than flying.  The idea that the plane would fly w/o you, so flying has less impact, is a fallacy.

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.

Well, alright, I'll try again.  Think of trains in vacuum tubes travelling really really fast.  Then remember that you don't have to support them on magnetic fields, which are  "expensive".  You can do it with air bearings, yes, even in a vacuum tube, just by pumping the air back into the bag and not letting most of it leak into the vacuum tube.  Thus you have huge load capability and essentially unlimited speed.  and the energy requirement is trivial relative to the airplane doing the same job, since what you put in to get the train going you can mostly get back when it is slowed to a stop.

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?

There's a great source of data here:

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
Response      1.1                14449       13642     (e.g. svcs for senior citizens and disabled)
Vanpool       6.3                8568        1362

Transit         9.1                37492       4127
Intercity                                         932

Commercial    95.8               354631      3703
Gen Aviation                                      10384

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

Simmon's is right. Near the top of the public policy wish-list should be movement of freight by rail and water instead of by truck.
The train/bus data is an average of places with high and low density. The more people you can get on trains and buses the better.
I just did a calculation this weekend on the same topic.  I also checked the fuel efficiency of the German high-speed ICE trains.  Their stated efficiency, for a half-full train, is about 1100 Btu/passenger-mile.
In the refining process one grade is taken at a higher level than another in the cracker, so, out of a barrel of crude, you take all grades, as a rule, depending on crude in the process, giving perhaps, 10% jet (kero) 35% gasoline, other products, and what falls to the bottom of the cracking process is what is used to make tar (ashphalt). Obviously, it is real difficult to determine ratios of what products are derived from a barrel of crude, but it takes several barrels of crude to make enough gas to make the amount to fill up a Civic Hatchback.
If that was true, we would not be able to consume 45% of our petroleum products delivered as motor gasoline.

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.

We have a 10 gallon tank in our Civic hatchback, I think.
I answered this question in some detail earlier in the thread (Jack on Sun Oct 02 at 1:04 PM EDT)

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.

This is not 100% germane, but I think it adds flavor to the discussion. I was riding an Airbus 319 just a few days ago and decided to ask the pilot about peak and average fuel consumption. He told me the following:

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?

Oh, one more thing about airplanes and fuel. While pondering the fuel consumption information, I started thinking about what happens to the energy being burned. Much of the work against gravity is recaptured when the plane comes down. Some work is used to heat the atmosphere directly. Otherwise, all the work, as far as I can see, by far the largest amount of work is done against atmospheric friction.

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!

Actually, you are reducing friction by climbing to 24,000 feet. The air is thinner up there. And, there is more room and less traffic up there than on the I-95 freeway.

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:  )

At the risk of being nit-picking, when a plane descends, it DOES recover a significant portion of the energy that was expended in climbing to the given altitude. The reason is that a portion of the potential energy accumulated in climbing (mgh) is coverted into horizontal movement as the plane (partially) glides during its descent.

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.

Friction is indeed the main issue, at least for longer flights.  And it can be drastically reduced by simply flying slower!  The energy needed to overcome friction to cover a given distance is proportional to the speed SQUARED.  Combine a lower speed with good streamlining (and airliners are already pretty good on that) and it shouldn't be much different from trains.  Sailplanes can fly for hours with no engine at all, making use of natural rising air (e.g., thermals).   In the process a sailplane extracts a power of roughly 5 HP from what is essentially solar energy.  (For those of you who don't know, sailplanes, also known as gliders, typically carry one person, and are flown for sport, not transportation.  Their key to low friction is the long, slender wings.)  The point is that riding on air is not inherently energy intensive.  Our "hurry up and wait" lifestyle is.
Yeah.  I keep saying unnecessary just-in-time convenience is a big waster of energy and will have to give sooner or later.

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.

Alas, the power required to push a vehicle thru air is proportional to speed cubed (ignoring mach number effects).  Power (like watts) is proportional to force times velocity.  the force (drag) is proportional to speed squared, and you then have to multiply that by velocity to get power.  If you are after total energy required, that's power times trip time, which is velocity cubed divided by velocity which is indeed velocity squared (not including a whole bunch of complicating factors that don't fit on the napkin but may swamp the whole shebang)

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.

I agree that there are many externalities to consider. Comparing these external costs is not a simple matter.  And I think we can all agree there are extremely few people who would opt for the bus or the train, when traveling across the American continent, when the same price gets them a plane trip.  I suspect the train is primarily the choice of those with phobias about flying.  And other than that, I wonder whether there are few if any people who travel across the US on bus.  The San Diego to New York route I looked up at Greyhound is a compilation of shorter hauls that are more than likely cost-competitive to flying.  E.g. a San Diego to Las Vegas bus ride costs me $50 while a plane ride costs be about $125.
Though this discussion took place last year, I found it while trying to decide if it were better ecologically to fly or drive from Colorado to Seattle. This discussion and everyone's input is very interesting. Here are my thoughts on this...
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.