5 Similarities Between PRT and Cars

Over the years, transportation planners have looked at a lot of different variations on the basic PRT concept of autonomous vehicles moving on a rail system between locations. But perhaps the best state-of-the-art model of the technology is at Heathrow Airport outside London, which in 2011 unveiled a pod car system built by Ultra, a British company. The system consists of 21 battery-powered, driverless, zero-emission vehicles, each capable of carrying four passengers and luggage along a 2.3-mile (3.7-kilometer) route between the airport garage complex and Heathrow's main terminal in five minutes' time [source: Ultra].

For passengers, riding in an Ultra pod beats rushing to flag down a shuttle bus and then having to squeeze into a compartment already jammed full of surly strangers. Instead, they simply touch a computer screen at any of the multiple stations along the route to summon one of the pods, which are dispatched by a central computer and distributed to stations according to passenger demand. And the pod is designed to accommodate about the same number of people who typically would ride in a standard sedan, so there's no overcrowding. Plus, passengers can choose who they ride with [source: Ultra].

The pods are actually built largely from off-the-shelf automotive industry components, and include features often found in cars, such as front-wheel drive, rack-and-pinion steering, double-wishbone suspension on the front and rear, and wheels equipped with tubeless radial tires. If you're not conversant in gearhead jargon, just rest assured that riding in a pod feels about as smooth as riding in a car. And since you can sit facing your fellow passengers, it's actually more comfortable to have a conversation, and there's more freedom of movement in case you need to stretch your legs [source: Ultra].

The Ultra PRT system at Heathrow moves at a speed of around 25 miles an hour (40 kilometers per hour), which is only slightly slower than the maximum speed limits allowed on the streets of major cities such as New York and Chicago. And when it comes to getting around in a congested urban area, a PRT system might even get you there faster. PRTs would move along their own railways, isolated from other vehicle traffic, so passengers wouldn't have to worry about getting caught in traffic jams. And once a rider summoned a PRT vehicle and got in, that pod automatically would merge into the railway and closely follow the pod in front of it. Since all the vehicles on the system would be tied into the same computer network, you wouldn't have to worry about another driver cutting you off or causing a fender bender, and you wouldn't have to be concerned about traffic lights.

"It's like an automated taxi that runs on its own roadway and doesn't have to stop," Peter Muller, president of PRT Consulting, a Colorado-based company that works with cities and agencies to study personal rapid transit feasibility, told CNN in 2011.That's one reason some cities are looking to build PRTs in currently-congested areas; San Jose, Calif., for example, is looking at building a PRT system to connect the city with a local airport and a proposed train station. But Muller told CNN that his company also has been developing blueprints for future car-free cities where residents would rely entirely upon pods [source: Almasy].

The Ultra PRT system features lots of electronic bells and whistles. A crash avoidance system equipped with sensors is programmed to spot other vehicles. A wireless communication setup allows passengers to communicate both via voice and data with the central station. And flat-panel video screens and audio speakers play music and video clips and display information for travelers. There's also the option of installing a "smart card" system that allows passengers to store their musical preferences on their personal cards, so that when they get into a pod, it'll automatically fire up a specific tune [source: Ultra].

But PRTs would be a little ahead of the curve of today's cars when it comes to wireless electronic gadgetry, since unlike the latter, they would be driverless robotic vehicles, part of a fleet operated by a central computer network. Automakers actually have been looking into developing similar networked systems and robotic autopilots for cars that would operate on regular roads. One recent study by the German automaker Opel concluded that even connecting 5 percent of cars to such a system would potentially save hundreds of millions of dollars in fuel costs, because it would enable traffic to flow more efficiently [source: Battles]. But there are undoubtedly a lot of kinks that have to be worked out before we unleash robot cars on the streets, where they'll have to contend with reckless human drivers akin to the speed-loving "little old lady from Pasadena" who was immortalized in the 1960s Beach Boys song. Pods on a rail system, in contrast, can rely on remote control with less potential for mishaps.

We spend an ungodly fortune on gasoline -- more than $4,400 per household in the United States in 2011 [source: Rooney]. Then there's the cost of maintenance, insurance and parking, assuming we can find spaces in crowded mall parking lots and urban garages. And don't even get us started about the environmental impact. According to a 2006 report by Environmental Defense, U.S. cars and light trucks emit the equivalent of 314 million metric tons of carbon dioxide annually. That's the amount of carbon you'd find in a coal train -- one that was 50,000 miles (80,467 kilometers) long. Americans account for 5 percent of the world's population, but account for nearly half of the world's automotive carbon emissions, which are a powerful contributing factor in climate change [source: DeCicco and Fung].

If you're concerned about protecting the planet and fighting climate change, you probably already are driving a hybrid gasoline-electric vehicle such as a Toyota Prius, or -- if you're really a hardcore green zealot -- a fully electric vehicle such as the Nissan Leaf. But PRT systems, whose vehicles are controlled by a central computer to operate at optimal efficiency, are even easier on the Earth. The Ultra PRT system at Heathrow, for example, reportedly produces 70 percent fewer carbon emissions than cars would and uses about one-fifth the energy required to propel a full-sized shuttle bus [source: Daly].

When you think public transit, you probably think clunky-looking vehicles like flex buses and old-fashioned trolleys. But Global's pod system at Heathrow, with its bullet-headed, gleaming metallic vehicles, affects a streamlined futuristic look that wouldn't be out of place in a cinematic sci-fi thriller [source: Good]. The Pinaforma-Vectus PRT concept is even more avant garde, with pods in a truncated wedge shape and floor-to-roof glass doors [source: Weiss].

Both existing and proposed designs for PRTs, in fact, look at least a little like bigger versions of the Mini Cooper and the Smart car -- or better yet, the "city" or "urban" concept cars developed by automakers, which have similarly blunted, streamlined shapes. One particularly PRT-like vehicle is GM's EN-V concept car, a podlike two-seater whose twin Segway-style wheels are powered by an electric motor running on lithium-phospate batteries. Unveiled at the Shaghai World Expo in May 2010, the EN-V has a lot in common with PRT systems technologically, as well. Like a PRT, an EN-V can drive in robot mode, with a central computer network controlling its movements. It also would be equipped with sensors to communicate with other vehicles and traffic signals, and a wireless Internet connection that would allow passengers to hold video conferences while on the move. The EN-V would be capable of much more complicated maneuvers than a PRT, since it wouldn't be on a rail system -- including the ability to make 360-degree turns on its twin wheels. However, like PRTs, the EN-V would require an elaborate infrastructure to operate [source: Scott].