When Heathrow Terminal 5 opens next year, a network of up to 18 driverless pods will ferry people between the main terminal and its car parks, where each pod will be controlled by an internal computer and onboard sensor systems.
Heathrow's network is admittedly modest: just 3.5km (2.2 miles) of guideway will connect car park and terminal. But it is the first public test of its kind. BAA has indicated that if the pilot is successful, it will extend PRT throughout the airport.
Once inside the pod you pick your destination and travel at about 20mph. On alighting, the pod waits for the next fare or is automatically rerouted to where there is most demand. As Russell Goodway, the former lord mayor of Cardiff once put it, PRT is "public transport that is waiting for you, rather than you waiting for it".
PRT was conceived in the 19th century, but it was the American Donn Fichter who began seriously pushing the idea with his book, Individualized Automated Transit and the City, in 1964 - although he says the idea was based on work going back to 1953 (see below). The UK planned extensive PRT networks for Birmingham and central London until 1971. Equivalent projects in France, Germany, Sweden, Japan and the US began in earnest before being commercially derailed.
Now, environmental concerns are driving a revival of interest. According to Advanced Passenger Systems, each vehicle uses just a quarter of the energy per passenger mile of a car. Some proponents predict PRT could be run on renewable energy, such as solar. But even with conventional electricity, Ultra remains attractive because its exhaust emissions are effectively zero.
PRT is good for a closed network such as an airport, but there are indications that it could soon wend its way into our towns and cities. Several local authorities are looking closely at PRT, and the one furthest down the line is Daventry in Northamptonshire. Its population of 23,000 is set to expand to more than 40,000 by 2021 as part of the government's strategy to build lots of new houses within striking distance of London.
Several Gulf states are thought to be developing PRT systems, as are the French. But the Dutch have hit an unexpectedly bumpy ride. Earlier this year, 2getthere (2getthere.eu), which was developing a driverless shuttle bus in Rotterdam, filed for bankruptcy.
In terms of capacity, PRT is expected to be at least as efficient as a stretch of motorway, but less efficient than a mainline railway. Lowson says the solution in city centres is to build overhead. But for the near future at least, PRT is likely to be developed as a complimentary transport, ferrying people around airports or large campuses.
After the UK, the most developed market for PRT is in Sweden. Two rival systems are competing to build networks in Swedish cities. Posco, a Korean company, is developing a system in Uppsala, while the Stockholm-based Skycab (skycab.se/eng) is planning three, including Arlanda airport, a university campus in Stockholm and the small town of Horfors.
Several PRT systems have already proved to be technically competent. The challenge is getting people to accept such a futuristic mode of transport and making them actually use it. Only then will the age of the podcar have finally arrived.
Personal Rapid Transport: the story so far
1953: Donn Fichter, a New York city transportation planner, begins research on personal rapid transport (PRT).
1967: Len Blake at the British Electrical Company begins developing Cabtrack, which planned a network of overhead guideways for Birmingham and central London. The project is shelved in 1972 due to cost and visual intrusion.
1967: Aerospace giant Matra initiates the Aramis Project in Paris. Development of the project runs for 20 years at a cost of 500m francs, but it fails qualification trials and is cancelled.
1970: Japan begins testing Computer-controlled Vehicle System (CVS), operating 84 vehicles at speeds up to 60kph. Public tests carry 800,000 passengers until government cancels the project under rail safety regulations.
1975: The Morgantown Personal Rapid Transit project is completed in West Virginia, connecting the city's five university campuses. Purists argue that it is light rail, not PRT, as it is too heavy and each pod carries too many people. Still in operation, it carries an average of 15,000 passengers a day.
2003: The prototype ULTra (Urban Light Transport) system from Advanced Transport Systems is certified to carry passengers by the UK Railway Inspectorate.
2005: ULTra selected by BAA for Heathrow Terminal 5. Planned to transport 11,000 passengers per day from remote parking lots to the central terminal area. BAA plans to begin operation by the summer of 2008 and to expand the system in 2009.