Companies developing and/or testing driverless cars include Audi, BMW, Ford, Google, General Motors, Volkswagen and Volvo. Google's test involved a fleet of self-driving cars -- six Toyota Prii and an Audi TT -- navigating over 140,000 miles of California streets and highways. A single accident occurred during one of the infrequent occasions when a human was driving. Another test of over 1000 miles was completed successfully with no human intervention

A driverless car (sometimes called a self-driving car, an automated car or an autonomous vehicle) is a robotic vehicle that is designed to travel between destinations without a human operator. To qualify as fully autonomous, a vehicle must be able to navigate without human intervention to a predetermined destination over roads that have not been adapted for its use.

Here’s how Google’s cars work:

The “driver” sets a destination. The car’s software calculates a route and starts the car on its way. A rotating, roof-mounted LIDAR (Light Detection and Ranging - a technology similar to radar) sensor monitors a 60-meter range around the car and creates a dynamic 3-D map of the car’s current environment.A sensor on the left rear wheel monitors sideways movement to detect the car’s position relative to the 3-D map.Radar systems in the front and rear bumpers calculate distances to obstacles.Artificial intelligence (AI) software in the car is connected to all the sensors and has input from Google Street View and video cameras inside the car.The AI simulates human perceptual and decision-making processes and controls actions in driver-control systems such as steering and brakes.The car’s software consults Google Maps for advance notice of things like landmarks and traffic signs and lights.An override function is available to allow a human to take control of the vehicle.

Proponents of systems based on driverless cars say they would eliminate accidents caused by driver error, which is currently the cause of almost all traffic accidents. Furthermore, the greater precision of an automatic system could improve traffic flow, dramatically increase highway capacity and reduce or eliminate traffic jams. Finally, the systems would allow commuters to do other things while traveling, such as working, reading or sleeping.