Computers are slowly taking over one of the most potent symbols of human independence: driving.
The US Government says that shift will make the roads safer and eventually free people to work, read or even watch a movie as they travel.
But in the wake of deadly manufacturer defects at Toyota and General Motors, analysts are raising questions about whether autonomous vehicles could hurtle into dangerous territory.
Last month, the National Highway Transportation Safety Administration took the first step towards requiring that new cars be equipped with sophisticated computers designed to communicate with other vehicles, with the aim of preventing accidents and, eventually, guiding cars through traffic.
Those systems are being field-tested in Michigan. Some other states permit fully autonomous cars to be driven on their roads - in California, Google's fleet has logged more than 800,000km without incident. Before the decade is out, Volvo and Nissan say, self-driving cars will be available to the average consumer in dealer showrooms.
"Decades from now, it's likely we'll look back at this time period as one in which the historical arc of transportation safety considerably changed for the better," said David Friedman, acting NHTSA administrator.
But while autonomous cars herald great promise, they also pose difficult policy questions. Who is liable, the driver or the manufacturer, if autonomous vehicles crash? Who owns the trove of data the cars generate? Should a computer steer a car off the road if a tree limb falls in front of it? What about a child on a bicycle?
And the prospect of manufacturer defects would become even more alarming in vehicles that rely heavily on complex computer technology.
"Cars are meant to be driven by people, not machines," said Joan Claybrook, a consumer advocate and former NHTSA administrator. "I have enough trouble trusting my computer, much less a computer to drive my car."
Last month, the American Justice Department fined Toyota US$1.2 billion ($1.4 billion) for covering up a sudden-acceleration problem that has spawned more than 400 lawsuits - which was closely followed by another huge recall. Earlier this month, the Japanese giant announced a sweeping recall that took 1.8 million cars off US roads and 40,000 in New Zealand. There were 6.4 million cars and trucks covered by Toyota's recall.
Meanwhile, GM is facing multiple federal investigations into an ignition-switch problem that has contributed to at least 31 accidents and 12 deaths in a decade.
Nine million vehicles have been recalled in the US this year, putting it right on pace to break the 2004 record of 30.8 million.
In both cases, the problems turned out to be basic and mechanical. But federal safety investigations into the defects were complicated by the millions of lines of computer code and advanced electronics that are already standard equipment.
"The reality is that the vast majority of accidents are caused by human error and computers are going to dramatically improve on people's driving," said Joshua Schank, president and chief executive of the Eno Centre for Transportation, a research organisation that has studied the challenges posed by autonomous cars. But "people are very nervous about the idea that computers could go haywire and cause us to die".
Researchers such as Schank tend to focus on the positive. In the foreseeable future, they say, self-driving technology will save fuel, cut pollution and reduce highway costs. As more cars become autonomous, they could safely tailgate, packing more vehicles into existing lanes and making traffic jams a thing of the past. Autonomous cars even have the potential to offer the disabled the freedom of the road.
the nissan leaf self-driving car.
The pace of change has been rapid. Just 10 years ago, a self-driving-car competition held by the Defence Department's Defence Advanced Research Projects Agency failed to produce a winner. Not a single entry was able to complete a 228.5km desert course between California and Nevada and claim the $1 million prize.
Fast-forward to 2007, when a team of researchers from Pittsburgh's Carnegie Mellon University tricked out a Chevrolet Tahoe with conspicuous sensors outside and advanced electronics inside. The SUV was able to follow traffic laws, merge into moving traffic, make its way through traffic circles and avoid other obstacles.
By 2009, Google was test-driving autonomous cars on busy highways. Last year, speaking at a ceremony after the signing of a bill allowing the testing of autonomous cars on California highways, Google co-founder Sergey Brin said: "You can count on one hand the number of years until ordinary people can experience this."
Manufacturers have also stepped up the pace of research. Some have established outposts in Silicon Valley intended to foster collaboration with the region's deep well of technology entrepreneurs and increase the pace of the re-imagined car.
"The metabolic rate of what happens here is dramatically different than what happens everywhere else," said Venkatesh Prasad, a technical leader with Ford's research and innovation group in Palo Alto.
Other work is being done in Michigan, the ancestral home of vehicle development. In Ann Arbor, University of Michigan researchers backed by a federal highway safety grant have outfitted 3000 cars with special sensors and wireless devices that allow them to exchange information with one another and with nodes mounted on traffic lights, at intersections and along curves on more than 100km of city streets.
Ten times a second, the cars and roadways "talk" to one another, relaying vehicles' location, speed and direction, and alerting drivers if their cars are going too quickly around a curve or if another car is erratically changing lanes or braking.
Researchers are combing through billions of messages passed through the network with an eye towards creating a robo-road system to guide driverless cars.
The University of Michigan is constructing a 12ha facility to serve as a test track for self-driving cars. The test area will allow engineers to see how autonomous cars perform in a complicated urban environment.
For consumers, researchers say, the car's transformation is likely to unfold in stages. Within the next decade, cars will be able to drive themselves, but people will still have the option to take over. After that? Some engineers envision vehicles that are little more than the equivalent of railway passenger cars, with no controls for humans.
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