States are passing laws allowing driverless cars, but they are finding it's not easy to write rules of the road for vehicles with no steering wheel or pedals.
Tech giant Google expects to roll out 100 prototype self-driving vehicles later this year, with the very real possibility the cars could go into production before the end of the decade.
And while the announcement comes as a pleasant surprise to self-driving vehicle proponents—who believe the technology could save lives, reduce traffic congestion and give mobility to those who can't drive—it's also triggered some serious concerns.
Among those taken off guard are various state regulators who now have to address the idea of having a small fleet of test vehicles rolling around that will have no steering wheels, pedals or any other controls a human driver could use.
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Nevada, Florida, California and Michigan have approved driverless, or officially, autonomous vehicles. California, where Google is based, is in the preliminary stages of writing its guidelines for driverless prototypes, which go into effect in September. But they currently "require that a human being be in the vehicle as a test driver," explained Bernard Soriano, deputy director of the California Department of Motor Vehicles. "Someone…ready, willing and able to take over should something go wrong."
That could cause a problem for Google if the only thing someone in the little prototypes can do is hit a button to bring a test vehicle to a stop.
"Google is going to have to manufacture those vehicles with steering wheels and pedals," Soriano emphasized.
That's not entirely a conflict with the Silicon Valley firm's plans, at least not initially.
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Looking like a cross between an old Volkswagen Beetle and a Smart Fortwo microcar, the first of the battery-powered self-driving prototypes will have conventional controls, Chris Umson, director of Google's Autonomous Vehicle project told NBCNews.
"Safety is critical," he said during an interview, adding that "the nut isn't cracked all the way," and that a lot of work remains to be done before the company is confident the prototypes will be able to wander public roads with just a computer in control. But the goal is to eliminate traditional controls from the vast majority of the prototype fleet. And that could pose a serious regulatory challenge.
For his part, the California DMV's Soriano didn't entirely rule out the possibility. Noting that "we have a good working relationship with" Google, he left open the possibility that the idea of going completely driverless is something that will be addressed once the state sees how well the earlier, more conventional prototypes perform.
Nevada DMV officials declined to discuss how they might handle a driverless Google car, but Umson said that likely won't be an issue, at least not initially, as Google intends to center testing in California.
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Longer-term, the company will want to reach out beyond California and could face a serious regulatory challenge—especially if it wants to go ahead and put its technology into vehicles that will actually be sold to the public.
How well they'd be accepted by motorists—regardless of state regulations—remains to be seen. A Harris Poll conducted last winter found only 12 percent of Americans said they wouldn't be worried about turning over driving duties to their car. More than half said they were worried about hackers getting into the car's computer, while 79 percent questioned whether the technology might fail at some point.
Of course, opinions could change, or so Google hopes, as its prototype self-driving vehicles start to roll across the landscape. And many of the basic technologies—such as collision warning systems with auto-braking—are already proving their ability to reduce crashes and save lives.
To reduce the risks, Google will initially limit its little cars to a top speed of 25 miles per hour. All will have emergency stop buttons. And they will feature soft front ends and flexible windshields that, Umson says, should be far more forgiving in the event one does hit a pedestrian.
—By CNBC Contributor Paul A. Eisenstein. Follow him on Twitter@DetroitBureau or at thedetroitbureau.com.