ATTLEBORO, Mass. (AP) — Turning onto Interstate 95, a Boston-bound driver notices an odd-looking car moving in sync with traffic. But unlike the rest of the morning commute, the car appears to have no driver— just a passenger happily surfing the Net on a laptop.

While that scenario might seem to suggest a George Jetson cartoon vision of the future, the reality of driverless cars sharing the highway with human commuters could be just a few exits down the road. A number of companies, including Google and Tesla, are already intensively testing cars that drive themselves.

"The car of the future isn't a concept— it's already here and pulling onto the interstate," said Elliot Katz, a San Francisco attorney whose clients include major U.S. automakers. "The manufacturers have the technology today."

All that's necessary, he says, is a little more technical refinement and for regulators to adjust rules and traffic regulations to accommodate them. That day could come within the next four to five years, he said.

Some advocates say roads populated exclusively by driverless cars would bring about a revolution in human mobility and safety, eliminating up to 90 percent of road fatalities now caused by human error.

But the advent of driverless vehicles also raises legal, ethical and insurance-related questions that will have to be sorted out before the public becomes fully comfortable with the idea of robot cars.

Some of those questions go to the most basic assumptions we have about automobiles.

"If it's a driverless car, then who's the operator?" Attleboro Police Chief Kyle Heagney said. "If there's a violation, who gets a ticket?"

Cars that can literally drive themselves also come laden with questions about liability. If there's an accident, is the owner or the manufacturer responsible?

Those questions remain to be resolved by lawmakers and insurance underwriters, who thus far have been hard pressed to keep up with fast-moving technological changes.

In the carmakers' laboratories, and to a lesser extent on public roads, however, driverless cars are already zooming ahead.

Manufacturers are already offering a number of features on new models that will be essential for future driverless cars, such as the ability to parallel park without driver input or apply the brakes automatically when an obstacle is detected.

Mercedes is introducing technology that will automatically keep a car driving within its lane even if the driver's concentration slips. And, Tesla Motors has an autopilot feature that will allow the car to do most of the driving in certain road environments, although the driver is still supposed to keep his or her hands on the wheel.

Ford Motor Company has announced it will put fully driverless vehicles, without steering wheels or pedals, on the road by 2021. And, ride sharing company Uber will soon start offering autonomous rides in Pittsburgh— although a live driver will be behind the wheel, just in case.

Despite dramatic progress recently, the road to putting driverless cars on the market hasn't been entirely smooth.

In an unsettling development, a Tesla Model S with Autopilot was involved in a fatal crash in May in Central Florida in which neither the driver nor the vehicle's radar system apparently noticed a truck that had turned onto the roadway. Tesla and the National Highway Transportation Safety Administration are investigating.

While many advances have already been made in automating the act of driving, none of the innovations introduced so far add up to a truly driverless car. Not completely, anyway. But, automakers and technology companies insist fully autonomous vehicles aren't far down the pike.

Steve Beringhause, chief of technology for Sensata Technologies in Attleboro, says it might take a while to solve all of the problems that will enable a consumer vehicle to operate autonomously on all roads all the time. But, he thinks a car that could drive reliably on limited access highways with human driver backup could be available to consumers as soon as 2020 or 2022.

Sensata is already working with a partner, California-based Quanergy Systems, on one of the key challenges to making a practical consumer vehicle with self-driving capabilities. They aim to be ready.

"We think we will conform to the timeline," Beringhause said in a telephone interview.

While automating some driving chores like parking is comparatively straightforward with modern computing and sensors, building a car that can reliably recognize and avoid obstacles, follow roads and obey traffic control cues in all circumstances is infinitely more complicated.

To do so, experts say, requires not just a fancy computer or highly evolved camera but overlapping layers of technology that will allow a car to perform reliably and safely.

"To be truly autonomous, vehicles will have to rely on multiple systems that tell it the same things," Beringhause said.

To acquire that information, test vehicles such as those developed by Google rely on a triad of sensing devices— video cameras, radar and a combination of radar and laser technology called LiDAR. The three are important because they provide different pieces of critical information a vehicle needs to make decisions.

For instance, radar might detect an object in the vehicle's path, but might not be able to distinguish a cardboard box from a compact car.

A video camera, by contrast, sees a child crossing the road, but can't deliver precise information on how the child is moving or the child's position relative to the vehicle.

LiDAR doesn't see a child, per se, but can detect and report its location and the range between the vehicle and the child in real time.

Working together, however, the three technologies aided by onboard computing coordinate overlapping data streams that enable a driverless car to make decisions mimicking those of a human.

One of the major barriers to building a consumer vehicle that's capable of driving itself is the high cost of LiDAR technology.

"The cost of existing LiDAR systems is pretty expensive, even as high as $100,000," said Sensata's Beringhause. "To get self-driving cars on the road, that cost needs to come down."

Sensata announced a partnership earlier this year with Quanergy to develop and commercialize the California company's LiDAR technology with an eye to high reliability and cutting costs down to size.

While automakers continue to pour billions into self-driving technology, many see equally daunting challenges in the form of infrastructure and a legal system that's tuned to human drivers.

"Our laws have not kept up with the pace of technology," said Tad Devlin, a lawyer and expert on autonomous vehicles. "My sense is that there will be a flood of changes."

So far, only Nevada, Florida, Michigan and California, along with Washington, D.C., have adopted laws providing for driverless cars.

The Massachusetts Legislature is considering bills that would permit testing such vehicles on public roads.

Besides changes to laws and traffic rules, others cite improvements in lane markings and traffic signals that might be needed to fully accommodate automated cars.

But even once the vehicles are fully permitted on American roads, questions remain.

Devlin says a number of variables could conceivably interfere with a driverless car's ability to operate safely, such as abrupt changes in visibility. And, liability in the event of a crash involving a self-driving car, he said, is "uncharted territory."

As more of the burden of driving shifts to the car itself, Devlin said, it's likely that more of the responsibility for what it does will shift from vehicle owners or drivers to those who make the vehicles.

It also could set up a legal quandary that could clog courts with product liability claims in damage cases.

"Probably who's responsible depends a lot on what the contract between the owner and the manufacturer says, and what you mean by an autonomous car," said Mansfield Police Chief Ron Sellon, who also holds a law degree.

"One thing you can be sure of: Lawyers will make out."

Not everyone is convinced that driverless cars are destined to take over American roadways.

State Rep. Steven Howitt, R-Seekonk, a member of the Legislature's Joint Transportation Committee, is a skeptic.

"I don't see the value of autonomous cars at this point," said Howitt, a car collector and sportscar fan. "People like their cars, and people like driving their cars."

Howitt said that while computer technology has made possible huge advances, like vehicles that are capable of parking themselves, he's not sure he'd trust one to drive.

"I'd feel a little uneasy if the car next to me didn't have a driver in it," he said.

Advocates like Katz have no doubts, however.

"Highway accidents cause 38,000 deaths a year, most caused by human error" he said. "Roadways filled with all driverless cars could reduce that number by 90 percent. I see that as a positive good."