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].