Underneath the proposed Zero Carbon Masdar City in Abu Dhabi (see this earlier post) will lie a hidden, vault-like space, in which a long dreamed of transportation system may one day carry passengers back and forth. It won’t be a bus, or rail system, or even a metro, instead, it will use small, autonomous pods that are more like taxis than buses.

The idea has been floating around for over 50 years and is called a personal rapid transit (PRT). Now that type of system is actually being built in Masdar City, although it is still in its planning stages. The Masdar PRT could finally become a world-changing idea.

People using PRT should get to and from their destinations more quickly and efficiently, and with none of the familiar hassles of mass transit (unhygenic, noisy and overcrowded).

The “per passenger” costs may also be cheaper. Trains may have a large capacity, but the fact is that they mostly run nearly empty. According to the US DOT, trains in the USA have an average occupancy of about 25 passengers - that’s the overall average when you consider all those off-peak times when (e.g.) a 160-passenger train carries only a handful of passengers. And this number would be much lower if trains were available all the time as PRT is.

PRT vehicles are light and only move in proportion to demand. A PRT vehicle might carry an average of only 1 person, but it’s only 500 kg’s moving to carry that one person. Compare this to 30,000 kg trains carrying an average of 25 passengers (more than 1,000kg’s of vehicle per passenger, double that of a PRT vehicle), and you can see the energy efficiency advantage of small vehicles. Furthermore, the non-stop travel of a PRT vehicle saves energy, and the automated, no-driver operation saves money.

Ariel View of the planned Masdar City

PRT was chosen for Masdar because it is cheaper and greener than other transit, while remaining very convenient. Almost all of the intra-city traffic will be PRT, including freight and garbage collection. The light rail line that slices through the center is mainly for connection to the airport and neighboring city.

When it comes to the issue of public transit in the emirate, money takes second place to local concerns over mass-transit systems, many of which are culturally based, including reluctance to pack women and men onto the same mass transport. Today, Abu Dhabi runs almost entirely on cars and taxis, but many transit planners consider the Middle East a prime area for PRT’s birth.

The plan for Masdar specifies an elevated pedestrian-only street level. Below will be an open space, averaging 18 feet in height, mirroring the layout of the streets above. That is where the city’s transit planners, led by a company called Systematica, hopes to place PRT pods.

To use the PRT, the locals would have to go down stairs or an elevator to the under-city level, where they would press a button to call a pod. The average wait time would be about three minutes, according to Luca Guala, an area manager for Systematica; the ride itself would likely take a maximum of about six minutes, since Masdar is only six square kilometers. Total time: less than 10 minutes.

That time could extend slightly at peak usage hours. In general, says Guala, PRT is better at moving people during low usage periods, when the denizens of other cities are used to waiting 30 minutes or more for a bus to come. But with the low carrying capacity of the pods, PRT can become slow when overloaded. “If you want to move huge masses of people, you need a strong system like a metro,” he admits.

Systematica proposed transport schematic for Masdar City

Then again, Masdar’s population is only intended to reach 50,000, and the city will also have a light rail line crossing it diagonally. The city will also be constructed such that most people already live close to where they work, so the PRT system won’t get overloaded the way it might in a standard city, where businesses are centralized.

Critics of PRT will argue that its true weaknesses lie in the qualities that have repeatedly proven it to be an unworkable system elsewhere. In many of the particulars, they’re right. Several large American cities, as well as smaller ones, have contemplated PRT (and some, like Ithaca, NY, are still considering it). While the most common reason for abandoning the idea is potential cost and fear over being the first to run an unknown system, there are other negative aspects.

Chief among those is that almost all PRT systems ever planned have involved rail lines, which were necessary to guide the pods. The difficulty of building rail in an existing development, and its outright expense, scuppered quite a few systems. But advances in vehicle guidance and Masdar’s peculiar construction mean that its PRT system will not need rail; the pods will run on regular tires and have their own streets, making it easier for a modern computer system to guide them.

ParkShuttle Group Rapid Transit at Schiphol Airport

The computer system itself, used for guidance, has also been a concern in the past. The Morgantown system built in the 1970s, while not even coming close to the complexity of an ideal PRT system, still needed a mainframe computer system to run its cars. However with todays computing power, that sort of power is now contained within the average smartphone, and the required computing power can easily be acquired off the shelf.

Taxis driven by humans might be cheaper initially, but over time, the cost of housing and feeding all the taxi drivers would be more expensive, and humans have their own set of faults they can bring to the party.

The company that would build the actual pods and guidance system, called 2getthere, already runs a sort of PRT system in Rotterdam, Netherlands, for cargo, and a Group Rapid Transit system at Schiphol Airport for shuttling back and forth between the terminal building and the car parks. The real challenge now is to see if they can effectively become the mass transit system of choice for a whole city.