Not all science fiction visions pan out. In his book, "Voyage to the Center of the Earth," author Jules Verne conceived of the Earth's core as a "forest of mushrooms."

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Will there be a new kind of taxicab?

The literary genre of science fiction has a good track reco­rd for predicting the future. H.G. Wells, for example, described atomic bombs in his 1914 book, "The World Set Free." And in the 1865 novel, "From the Earth to the Moon," Jules Verne wrote about manned space flight; he also mentioned that the aluminum rocket carrying the three-man crew required a speed of 12,000 yards per second to launch. In reality, the actual launch speed of the first aluminum rocket carrying a three-man crew in 1969 was 11,424 yards per second -- not too far off, considering Verne penned his book 104 years earlier [source: Discover].

Satellites, deep-sea submarines and in vitro fertilization -- all predicted by science fiction writers decades or even a century before they were realized -- are all well and good, but let's cut to the chase. What kind of traffic will we have to deal with in the next 20 or 30 years?

It's entirely possible that the vision of a future filled with dense, fast-moving traffic in both street and sky shared by such divergent modern science fiction authors as Ray Bradbury and Philip K. Dick will be realized. Consider this: The United States Census Bureau predicts that the years from 1999 to 2042 will see a 50 percent increase in the global population [source: U.S. Census]. This means that by 2042, the world population will reach 9 billion people. These people are going to need to get around, so it seems logical to assume that our cities' traffic will reflect that. If we peered into the future right now, we could see dense, quickly moving traffic. But look a little closer. Those aren't cars -- they're taxis. And the people inside actually look happy.

What's going on? Is there some kind of new taxicab in the future? If some of today's engineers have their way, there sure will be. Find out about their vision on the next page.

An artist's rendering of the Vectus PRT system.

Photo courtesy Vectus

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Personal Rapid Transit (PRT)

The transportation infrastructure of major cities would all but collapse without fleets of taxis. For example, in New York City in 2003 only about 25 percent of residents had a license to drive [source: Washington Post]. Public transit, like buses and subways, is also extremely important for getting people from point A to point B in urban areas. In Hong Kong, 80 percent of residents in 2005 used public transportation for their commutes [source: Taipei Times].

Both taxis and public transit have their drawbacks, however. Taxis are cars, after all, and belch their fair share of carbon dioxide into the air. And subways have prescribed stops, in contrast to taxis that'll take you anywhere you want to go. It's enough to make you wonder if there's any relief to the dilemmas presented by these two horrors of modern urban life.

One proposed solution is personal rapid transit (PRT). The idea for PRT goes as far back as 1953, when an American urban planner began hammering out the logistics of combining the privacy of taxicabs with the subway's ability to move massive amounts of people [source: The Guardian]. While the details of PRT systems have evolved alongside technology (such as the idea of using solar power to generate electricity for the systems), the basic premise has remained the same. 

Essentially, PRTs are systems of established rail lines on which small, electric-powered vehicles (often referred to as podcars) ride. They work like this: You go to the nearest station, press a button that calls the closest available car and wait. In short order -- a matter of only 12 seconds in the case of Advanced Transport Systems' ULTra pods -- a car will arrive [source: The Guardian]. In other conceptions of PRT, enough cars will be available at any time so you won't have to even wait at the station. Under either design, you get into the car, tell the computer where you want to go, and you're off.

PRTs are unique in that they're exactly what the name suggests -- personal. The car that arrives when you call it is yours (not yours and some stranger's). So PRT will be just what the doctor ordered for clinically xenophobic commuters. "Personal" also means that the cars don't stop until its passengers are delivered to their specified destination. They're also driverless, electric vehicles, and since they don't require humans to operate, PRT systems will run 24 hours a day [source: CPRT].

There are several competing visions for PRT. Some designs include elevated monorail lines with cars that run on rails or dangle from an overhead rail. Other engineers envision PRT systems as a network of narrow, ground-level highways adjacent to streets that carry cars that move on wheels. Some proposed systems are electric, juiced up from solar power. This is perhaps the optimal design, since 50 percent of all electricity in the United States is currently produced by burning coal [source: PBS].

If all of this sounds a bit far-fetched, don't worry: You're not alone. PRT has its detractors. But the concept of PRT also has plenty of proponents, and they're gaining traction. Around the globe, urban areas are testing PRT systems. Find out on the next page about some of the cons of PRT and how the kinks are being worked out in places like Abu Dhabi and Sweden.

Advanced Transport Systems' ULTra podcar on its test track in Cardiff, Wales, in 2002.

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PRT Test Sites

For about as long as the idea's been around, personal rapid transit (PRT) has had its critics and proponents. Naysayers call PRT proponents dreamers at best and unscrupulous hucksters at worst. And criticism of PRT has come from some surprising sources. One episode of the cartoon sitcom "The Simpsons" spoofed the Broadway musical "The Music Man" while simultaneously leveling what appears to be subtle condemnation against PRT. In the episode, a too-good-to-be-true monorail proponent comes to town and fleeces the people of Springfield out of tax dollars for a rail system they don't need and that doesn't work.

It's difficult not to draw parallels between the fiction Springfield of "The Simpsons" and some real urban areas. Cities like Minneapolis, Minn., and Seattle, Wash., have seriously entertained installing PRTs before ultimately abandoning their plans. It should be said, however, that none of these systems had the likes of Homer Simpson as conductor of the rail lines. After all, PRTs are run by computers. But opponents point out that these computers can crash. 

This is perhaps the biggest drawback of the PRT concept: the logistics of the worst-case scenario in unmanned PRT systems. One big problem that faces proposed systems on a large scale is capacity [source: TreeHugger]. If PRT replaces subways, buses and taxis in the future, it has to be able to accommodate commuters at rush hour at least as well as current methods of public transportation can.

And what happens when one car breaks down? Under the current vision of most PRT systems, cars will tailgate one another at constant speeds. To accommodate passengers, the rail systems must be packed with podcars. If one stops suddenly, cars behind it will follow suit, leaving possibly hundreds or thousands of angry commuters stranded. Anyone who's had the bad fortune of being stuck on a rollercoaster can commiserate with that picture.

PRT engineers and designers have taken a step back from attempting to implement their systems on a large scale (like in Minneapolis and Seattle) and instead have begun testing on small tracks and in confined applications. In Sweden in 2005, podcar company Vectus constructed a test track and is currently seeking permission with the Swedish Railway Authority to implement a PRT system in the city of Uppsala [source: Vectus]. A system designed by the British company Advanced Transportation Systems is in use in Terminal 5 in London's Heathrow Airport. The mile-long track transports Heathrow customers between the terminal and the parking lot in the company's ULTra podcars [source: BBC].

By far, the largest testing ground for a PRT system is found in the United Arab Emirates. Masdar City, a development under construction outside Abu Dhabi, is looking to become the world's first carbon neutral city. A big part of that goal will be the implementation of the development's zero-emission, solar-powered electric PRT system with 1,500 stops scattered throughout the city [source: NPR].

With the introduction of more capital and an increasing willingness among developers and urban planners to adopt PRT systems, the forecast for the concept has never looked sunnier. Ultimately, a future with PRT rests in the public perception of the reliability of the transportation systems.

For more information on transportation and other related topics, visit the next page.

Lots More Information

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Sources

  • Atler, Lloyd. "Personal rapid transit "a cyberspace techno-dream." TreeHugger. March 7, 2008. http://www.treehugger.com/files/2008/03/prt-techno-dream.php
  • Dodson, Sean. "Welcome to the transport of tomorrow." The Guardian. October 11, 2007. http://www.guardian.co.uk/technology/2007/oct/11/guardianweeklytechnologysection.news1
  • Morrison, Chris. "The next pod revolution." CNN Money. June 19, 2007. http://money.cnn.com/magazines/business2/business2_archive/2007/06/01/100050977/
  • Palca, Joe. "Abu Dhabi aims to build first carbon-neutral city." NPR. May 6, 2008. http://www.npr.org/templates/story/story.php?storyId=90042092
  • Powell, Michael. "Licensed to drive? Fuhgeddaboutit!; most New Yorkers do without wheels." Washington Post. August 19, 2003. http://www.highbeam.com/doc/1P2-286231.html
  • Rogers, Lucy. "Are driverless pods the future?" BBC. December 18, 2007. http://news.bbc.co.uk/2/hi/uk_news/7148731.stm
  • Yan-Chih, Mo. "Taipei focuses on public transport and a clean environment." Taipei Times. September 11, 2005. http://www.taipeitimes.com/News/taiwan/archives/2005/09/11/2003271216/print
  • "PRT: Go where you like, when you like non-stop." Citizens for Personal Rapid Transit. http://www.cprt.org/CPRT/Home.html
  • "Vectus in brief." Vectus Intelligent Transport. June 1, 2006. http://www.vectus.se/press/Media_Backgrounder.pdf
  • "World population information." U.S. Census Bureau. May 20, 2008. http://www.census.gov/ipc/www/idb/worldpopinfo.html