We’re frequently bombarded with stories of how robot cars will soon roam the streets — news that some people dread and others welcome. But missing from these accounts is an answer to this big question: When?

The answer from one expert is five years. “I think it's going to happen really, really fast,” says Tim Huntzinger, a professor in the transportation design department at ArtCenter College of Design in Pasadena, California. “As soon as one person stands up and makes a billion dollars doing it, there will be a whole bunch of other people that will climb on right afterward.”

But other experts say it will be much longer before fully self-driving vehicles — what the U.S. Department of Transportation calls level 5, or Full Automation — are widely available. The real challenge will come from the complexity of integrating autonomous cars into real-world conditions. Though the technology may soon arrive, it’ll take time for regulations — and drivers — to catch up.

Current self-driving capabilities

What Huntzinger says will be available in just five years is a car you can climb into and say, “‘take me to the store,’ and it figures out where the nearest store is and takes you there.” But many self-driving features have been available in cars for years, such as automatic braking and adaptive cruise control, which adjusts your preset speed if the vehicle ahead is going slower.

“ I think it's going to happen really, really fast.” Tim Huntzinger , Transportation design professor

Currently, the major carmakers, and Tesla, a maverick in self-driving cars, are positioning themselves with extensive research and development for the transition to autonomous cars. New Tesla models offer a Full Self-Driving upgrade option — but this will be activated only upon software validation and regulatory approval. Meanwhile, Cadillac’s 2018 CT6 includes a Super Cruise system that steers and brakes the car, allowing hands-free driving on limited-access freeways.

‘The real world is messy’

But Tesla also suffered a setback last year when a self-driving Tesla Model S was involved in a fatal car accident in Florida. The crash points to a key challenge in the widespread adoption of driverless cars: the messiness and unpredictability of driving in the real world.

On a California road trip in a Tesla Model X equipped with an early version of Autopilot, Josh Sadlier, senior manager of content strategy at Edmunds.com, says he drove for several miles at a time without touching the steering wheel. But while traveling at 70 mph on a rural stretch of Highway 101, he felt the car veering off the road when the lane marking on a bridge suddenly disappeared. He says if he hadn’t quickly steered the car he would’ve hit the railing.

“It's one thing for self-driving cars to work on perfectly paved streets where all the variables are consistent, but the real world is messy,” Sadlier says. “How close are self-driving cars to being able to cut through the mess and keep you on course without crashing?” He predicts that self-driving cars won’t be here for “decades, if you mean cars without steering wheels that let you read your Kindle on the way to the mall.”

Letting computers take the wheel

John O’Dell, editor of TheGreenCarGuy.com, estimates that in 2022 driverless technology will be fully tested by tens of thousands of real-world miles. But, “I don’t think the rules and regulations will be ready by then, and I don’t believe drivers will be, either,” he says. “It takes a bit of retraining to get to the point that you can fully surrender control and let the computers do the work.”

Unlike Sadlier’s experience, where he was able to correct the car’s course, O’Dell notes that Google testing showed that drivers became too comfortable with letting the car drive itself and weren’t ready to take over in an emergency. “So instead of taking control, they crashed,” O’Dell says.

While it’s a sad reality that there will be accidents when self-driving cars are phased in, Huntzinger is quick to point out that human drivers are far from perfect. Automobiles and human error are already responsible for hundreds of thousands of deaths worldwide every year, he says: “We will get to the point where it will just make more sense to put the computer in charge. Even if it's fallible, it will be better than people.”

Who will take the first step?

However, Huntzinger predicts that the first fully self-driving cars will come not from a major car manufacturer, or even from Tesla, but from a startup we haven’t heard of yet. Though in some respects the technology is here — you can watch videos of Google’s driverless cars scurrying about — large companies with deep pockets are afraid to use it, he says. The danger is in taking that first step and testing self-driving cars in the real world with real — and often inattentive — drivers.

“Beta testing is fine for software,” Huntzinger says. “But as soon as you begin dealing with transportation and things that will actually kill people or go wrong, it becomes a much more complicated problem.”