the dawn of the new age of driverless cars Never distracted: In critical situations, driver assistance systems react more quickly than humans ever could. The journey begins conventionally, with the driver turning the wheel to ease the car out of the driveway. But then he flicks a switch and raises his hands in the air. The laptop in the passenger seat is in charge now. On a busy Saturday evening in suburban Berlin, the modified Volkswagen Passat drives itself down a tree-lined street crowded with pedestrians. Spotting a woman on a bicycle ahead, the car veers left to give her a wide berth, and then slows as a minibus filled with children pulls out from the kerb. The car's machine driver judges the minibus' speed and decides on a surge of power to overtake. Germany is at the forefront of a global race to develop the world's first driverless car. Devised by a team at the Free University of Berlin, the Passat is a highly advanced autonomous car, capable of navigating a safe path through unpredictable city traffic. It sees the world through a spinning silver cylinder mounted on the roof, a laser scanner, which generates a million data points per second to give the car's computer a real-time map of its surroundings. Cameras and radar sensors provide further detail, alongside an ultra-precise GPS based on the navigation systems used in aircraft. It will be many years before a car this sophisticated is commercially available. But Germany's luxury car makers have begun introducing an array of autonomous features that enable some of their leading models to drive and steer themselves. Rather than the sudden advent of robot vehicles, car makers believe autonomous driving will be introduced gradually. Daimler, which owns Mercedes-Benz, predicts that at low speeds - such as in traffic jams or parking - cars will operate with full autonomy "in a matter of years." At higher speeds, several manufacturers plan for highly automated driving within the structured environment of a motorway. The latest Mercedes S-Class is the most significant advance yet in automated driving for the mass market. The luxury sedan comes equipped with a camera that scans the road ahead and an array of radar sensors. The images it captures are analysed by an algorithm, allowing the car to alert the driver to danger and take corrective action itself if necessary. "In critical situations, the driver assistance systems in the car react more quickly than humans ever could," says Professor Ralf Herrtwich, director of driver assistance at Daimler. Unlike drivers, they are never inattentive. The aim of greater automation is not to take away the pleasure of the open road but to save motorists from some of the tasks that make driving a chore. Customers would be relieved to hand over to a computer "in situations where driving simply isn't enjoyable, for example in a traffic jam on the daily commute to work," a BMW spokeswoman says. Raul Rojas, a professor of artificial intelligence at the Free University of Berlin who leads its autonomous car project, has a more ambitious vision. He predicts the public transport of the future will be fleets of robot taxis, cheaper and safer than the human kind, operating for 24 hours a day without fatigue. In a few years' time, Professor Rojas suggests, people will use their mobile phones to summon a robot taxi, dropping it off at their destination ready for the next passenger. There are still technical barriers to the mass production of automated cars. The key problem is vision. The laser scanners used by the Free University's car cannot pass through a solid barrier, so a pedestrian stepping out from between two parked buses would be invisible until the last moment. An automated car "does not just need to watch out for other cars," Professor Herrtwich says. It needs to check for pedestrians and cyclists, for lanes, stopping lines, traffic signs, and traffic lights. It needs to understand that a lane ends in a few hundred metres or that there is a stalled vehicle on the highway ahead of it. This technology does not just need to be reliable, but affordable within the budget constraints of a typical mass production vehicle. The Free University's team is working on improving the computer's vision, but face a huge challenge replicating the human ability to see. "Almost a fifth of the brain is just for image processing," Professor Rojas says. There's lots of things that we don't yet understand about how human vision works. Computer visual recognition is still very, very primitive. There are legal barriers too, as the Vienna Convention of 1968, the global legal framework for driving, requires that motorists are in full control of their vehicle at all times. Another vital question is legal liability, as a BMW spokeswoman says: "Who is responsible for an automated driving system in case of an accident or failure?" Before fully driverless cars become a reality, there is one more problem to solve. The relationship between automated vehicles and human road users is the greatest challenge of all. Machines lack our social skills. Computer-driven cars cannot judge, for example, whether a pedestrian waving at them from the kerb is urging them to stop or go. "That's the last frontier: predicting human behaviour," Professor Rojas says. Nobody can do it yet, in a reliable way, but it has to be done for autonomous cars to be safe.