21st Century Green Transport
Tue Jan 15, 2008 at 04:11:11 PM PDT
One of the things I love about Al Gore (and find lacking in the current crop of presidential candidates) is his wonkish visionary interest in future tech. We really need leaders who can see farther than eight years ahead.
This paper from 1998 was futuristic enough that it still isn't dated. It takes a long-term look at our transportation infrastructure options, beginning with fuel sources, and considers what sort of green people movers would be possible.
There's more...
The full article is here if you prefer to dive right in. The New York Times resurrected it recently (a public survice); their piece on it is here. From the intro to the paper:
We envision a transport system producing zero emissions and sparing the surface landscape, while people on average range hundreds of kilometers daily. We believe this prospect of 'green mobility' is consistent in general principles with historical evolution. We lay out these general principles, extracted from widespread observations of human behavior over long periods, and use them to explain past transport and to project the next 50 to 100 years.
The authors took their historical approach to the future after noting that transportation infrastructures take a century to develop:
A century or more is the rational time for conceiving a transport system. The infrastructures last for centuries. They take 50-100 years to build, in part because they also require complementary infrastructures. Railroads needed telegraphs, and paved roads needed oil delivery systems so that gasoline would be available to fill empty car tanks. Moreover, the new systems take 100 years to penetrate fully at the level of the consumer. Railroads began in the 1820s and peaked with consumers in the 1920s.
Unlike some future tech proponents, they didn't look at just one solution, but accepted the need for a range of transportation modalities:
We discuss serially and in increasing detail railroads, cars, aeroplanes, and magnetically levitated trains (maglevs).
They are remarkably sanguine about the prospects for transporation:
Fortunately, during the next century we may be able to afford green mobility. In fact, we can clearly see its elements: cars, powered by fuels cells; aeroplanes, powered by hydrogen; and maglevs, powered by electricity, probably nuclear. The future looks clean, fast, and green.
This persuasive paper is well worth reading for its details. Its most interesting section, to me, concerns maglev trains. While cars and planes will continue to be with us, but with different fuels, maglevs represent something new and different: the next century's new mode of travel. Like the car (which created the suburb), the maglev train may have a huge impact on settlement patterns all over the world. Here are excerpts to give you the flavor:
Maglevs ... can be fully passive to forces generated by electrical equipment and need no engine on board. Maglevs also provide the great opportunity for electricity to penetrate transport, the end-use sector from which it has been most successfully excluded.
...speeds in excess of 800 km/hour and in low pressure tunnels thousands of km per hr.... Constant acceleration maglevs (CAMs) could accelerate for the first half the ride and brake for the second and thus offer a very smooth ride with high accelerations. ... The system would store the energy recovered from braking trains locally and re-deliver it to accelerating trains. Recovery could be quite good with linear motors. High-temperature superconductors in fact could permit almost complete energy recovery in deceleration as well as hovering at zero energy cost. The external grid would provide only, on a quasi-continuous basis, the make-up for the losses....
The neat solution is partially evacuated tubes.... Tunnels also solve the problem of landscape disturbance.... Because the vehicles will be quite small, they would run very often. In principle, they could fly almost head-to-tail, ten seconds apart.
Ah, yeah. The operative words here being in principle. Personally, I wouldn't want anybody following me ten seconds behind down a tunnel at "thousands of km/hr". At least not if a computer was involved. (I'm a programmer.) But I like their brashness, and this internet metaphor:
In essence maglevs will be the choice for future Metros, at several scales: urban, possibly suburban, intercity, and continental.
The comparison is with the Internet -- a stream of data is broken down into addressed packets of digits individually switched at nodes to their final destination by efficient routing protocols.
The best thing about the paper is how grounded it is throughout in energy realities. For example:
Planes propel by pushing air back. Momentum corresponds to the speed of the air pushed back, that is, energy lost. Maglevs do not push air back, but in a sense push Earth, a large mass, which can provide momentum at negligible energy cost. ....reduced by 1-2 orders of magnitude.
Because maglevs carry neither engines nor fuel, the weight of the vehicle can be light and total payload mass high. ... [Instead of] heavy images of trains and planes [think of] a very light envelope suspended on a moving magnetic field.
A constant acceleration train in a partially evacuated (low-pressure) tunnel has inverse-logarithmic travel times (like a starship):
The trip from Wall Street to midtown Manhattan might be 1 min, while from Heathrow Airport to central London might be 2-3 min. For CAMs transit time grows as the square root of distance, so 500 km might take 10 min and 2500 km 20 min.
Travelling in a CAM at 0.5 G for 20 minutes, a woman in Miami could go to work in Boston and return to cook dinner for her children in the evening. Bostonians could symmetrically savor Florida, daily. Marrakech and Paris could pair, too. With appropriate interfaces, the new trains could carry hundreds of thousands of people per day, saving cultural roots without impeding work and business in the most suitable places.
Seismic activity could be a catch. In areas of high seismic activity, such as California, safe tubes (like highways) might not be a simple matter to design and operate.
Ya think? In Califonia where I live, I suspect evacuated above-ground tubes also have a future.
The principle omission in this article may be discussion of lower-speed maglev systems that do not require a tunnel at all. I suspect we'll also be riding above ground in small vehicles on maglev railways that resemble cable car ski lifts. These could lift our local roadways up and off the surface, so they don't bisect our landscape or render the land under them useless. Imagine today's major surface streets and interstate highways as elevated frictionless lanes, in which vehicles move silently overhead except for a slight woosh of displaced air. The same advantages of low vehicle weight, no on-board engine, and the ability to use electric power apply. Moreover, the towers and rails of the system replace our current power transmission towers and local power poles, serving as the electrical grid itself. (The last few blocks to your house, hopefully, is underground and out of sight.)
The authors are rather sanguine about the future of transportation, and that's good to see:
Although other catches surely will appear, maglevs should displace the competition. Intrinsically, in the CAM format they have higher speed and lower energy costs and could accommodate density much greater than air. They could open new passenger flows on a grand scale during the 21st century with zero emissions and minimal surface structures.
Once again, I recommend the full article, especially if you enjoy the technical details.
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