Future Transportation

Barring some remarkable change in the world, we are going run out of oil in my lifetime. I don’t mean that we will literally run out of oil; I mean that it will become too expensive to use for ordinary tasks such as selling it in the form of gasoline for cars. There seem to be a number of alternative for cars, ranging from batteries to biofuel to liquified natural gas. So cars in the future will most likely continue to exist in much the same form they have now, perhaps somewhat smaller and lighter and with less range but not radically different.

What I wonder is whether there is a good alternative for jet fuel. We in the western world have become accustomed to relatively casual flying. We can get to any part of the world we care to go to, by simply hopping on a plane. When jet fuel is no longer easily available, will we lose that ability? Will flying become restricted to the very rich or very important?

In many ways that might be a good thing, making the world larger again after it has spent so many years becoming smaller. In many other ways, of course, it would be a bad thing. Every time I fly with my daughter I wonder how often she will be able to fly when she is an adult.


  1. ncm said,

    March 26, 2008 @ 6:48 pm

    Hydrogen seems much more practical for jets than for cars. First, the transport and storage problem is much simpler, if only because there are way fewer airports than gas stations, and the fuel is handled by pros. Second, existing jet engines happily on hydrogen, so only the tankage, fuel delivery, and control computers would need retrofitting, not the expensive turbines. (In practice this might mean new airframes with engines cannibalized from older planes.) Third, the fuel load they can carry is limited by weight more than by volume, possibly favoring hydrogen.

    Maybe in a few years hydrogen-powered ballistic scramjets will be cheaper to operate, over interesting distances, than aircraft. After all, much of the cost of operating an airplane is in moving the air out of its way.

    Of greater concern to me is a practical fuel for tractor-trailers. You’d notice if the planes stopped flying, but you’d starve if the trucks stopped.

  2. graydon said,

    March 26, 2008 @ 9:39 pm

    I expect we’ll see a reduction in the feasibility of travel. But it’s hard to tell for sure: the spectrum of plausible futures runs the gamut from “rapid adaptation, optimization and efficiency improvements make energy/population/ecology crunches non-issues” to “total collapse of technological civilization followed by unpleasant remaining days in stone-age conditions, brought to an end by being hit over the head with a club”. Many variables, hard to know.

    I agree with ncm, though: running out of oil has much more dire consequences than jet transport. More dire indeed than running low on tractor-trailers: hit the petroleum supply hard enough and we may not be able to produce enough nitrogen fertilizers to *grow* the food, much less ship it.

  3. etbe said,

    March 31, 2008 @ 4:38 am

    ncm: Most trucks can be replaced by trains – if you have a well designed train network or time to build one. Pity that the US has no useful train network or the organisational ability to build one before it’s too late (a LOT of Diesel fuel is needed to build train lines but they can last for over 100 years with little upkeep).

    I was under the impression that there was little spare space on most aircraft. This cost of moving the air out of it’s way is a function of the volume… Also the tanks used for hydrogen are significantly heavier than tanks for liquid fuel.

    Ian: You can travel internationally by ship. It’s not widely known but many cargo ships have a small amount of passenger capacity. Ships can significantly increase their fuel efficiency by reducing their speed and there is a lot of work on using alternate fuels for ships (including wind power).

    In future I expect to travel from Australia to Asia via ship and then travel by train to everywhere in Europe. It seems unlikely that the US will be a desirable place to visit once oil supplies run low.

  4. Ian Lance Taylor said,

    March 31, 2008 @ 9:28 am

    Thanks for the notes.

    I’m not sure that ship travel really substitutes for air travel.

    I hadn’t thought about hydrogen for jet engines. I don’t know enough about it.

    Tractor trailers will run fine on biofuels.

    I think the fertilizer problem is overrated. First, it’s really a question of energy, not oil per se. If we had, say, fusion power, we could continue to produce fertilizer. Second, high energy fertilizer is permitting farmers to grow monoculture crops. That has its own drawbacks. We know enough to grow about as much food via crop rotation. We wouldn’t have as much corn, but we have a vast surplus of corn anyhow. I think we’ll be OK.

    I used to worry a lot about plastic after all the oil is gone, but there is an impressive array of substitutes appearing. None of them are as good, but they seem to suffice for most uses, and they will improve.

  5. ncm said,

    March 31, 2008 @ 10:33 pm

    What biofuels did you have in mind? Converting the entire present U.S. corn crop to alcohol suffices to power

  6. ncm said,

    March 31, 2008 @ 10:34 pm

    … 12% of present automobile traffic, never mind trucks.

  7. Ian Lance Taylor said,

    April 1, 2008 @ 6:46 am

    First, corn is not a very good source of biofuels. We only currently consider using corn as a biofuel because our broken agricultural policies encourage a vast over-supply of corn. Although at least using it as biofuel is better than turning it into corn syrup and encouraging the rise in diabetes. A much better source of biofuel would be something like switch grass, which grows by itself without requiring a high energy input. It seems safe to predict that we will work out how to implement this.

    Second, it’s clear that there is no single alternative to oil. We shouldn’t dismiss biofuel because it can’t completely replace gasoline. I think that it probably can replace gasoline for the specific case of tractor-trailers–along with, as etbe said, more use of trains for long distance transport. Biofuels aren’t going to be the fuel source of the future for cars, at least not if we use cars as we do today. If we continue to use cars more or less as we do today, I predict that they will be largely electric, largely fueled by nuclear power. They will not be as powerful or as flexible as today’s cars, but, so it goes.

  8. ncm said,

    April 1, 2008 @ 11:35 am

    Also, I’m not worried about plastics. There will always be enough oil for essential plastics, albeit at a higher price. Once non-polluting alternatives to oil and coal catch on, the price might even crash as demand fades.

    I’m very bullish on adding flywheels to trains.

  9. etbe said,

    April 2, 2008 @ 6:18 pm

    ncm: Diesel-electric trains are already quite efficient. If they were to optimise the routes (more direct lines and more express trains for cargo) and use the latest technology for generators, electric motors, and direct-rail Diesel engines then they would probably be efficient enough that there would be little need to try and improve things.


    The above wikipedia page states that Bio-diesel is less energy dense than petroleum based Diesel fuel, and that Ethanol is less energy dense than “Gasoline”. The lower energy density leads to less efficiency overall (more space for fuel means less cargo capacity in passenger vehicles). Of course the difference between Diesel and bio-Diesel is small, but the difference between Ethanol and Gasoline is significant.

    Nuclear power is not a viable option. The expenses of building, maintaining, and decommissioning nuclear plants are significant. The terrorism related problems are also worth noting.

    If linked into continent wide grids by HVDC wind power has the potential to supply the vast majority of electricity use. Smart-meters to allow reducing residential electricity use at times of high-demand/low-supply have already been developed. The practice of cutting electricity to factories at times of high demand (and therefore high wholesale price) has been used for a long time.

    While wind power varies a lot in a small area, over an area the size of Australia or mainland USA (even excluding Alaska) the variation is small.

  10. erin said,

    April 2, 2008 @ 8:22 pm


  11. Ian Lance Taylor said,

    April 2, 2008 @ 8:51 pm

    Several countries use nuclear power quite successfully. I think that if nuclear power is not an option that we are in serious long-term trouble. I’m skeptical about deploying very wide scale wind production.

  12. Ian Lance Taylor said,

    April 2, 2008 @ 8:55 pm

    The railbike looks cool. In my younger days I enjoyed walking train tracks. You get a very different perspective on a city by walking the tracks.

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