Most of the technology needed to make driverless cars already exists. Despite this, it’ll be at least 20 years before they are widely available to weary road warriors.

Meanwhile, efforts to bring fully automated vehicles to market are far enough along to catch the eyes of Wall Street investors, who are not about to sit idly by while the industry sorts out the many hurdles -- legal and social as well as technical -- it still faces.

Many luxury and mid-market cars already offer advanced driver-assistance systems such as advanced cruise control, which keeps the car a safe distance from traffic ahead, blind-spot warning, and other features that were once exclusive to ultra-luxury vehicles.

The industry is moving quickly. In less than a week, BMW AG BMW, -4.80% unveiled a car that can park itself, Tesla Motors Inc. TSLA, -4.01% Chief Executive Elon Musk said he’s personally testing an enhanced autopilot feature for the company’s electric cars, and the Chinese web company Baidu Inc. BIDU, -1.57% was reportedly working on a driverless car to challenge the one under development by Google Inc. GOOG, -3.05%

The road to fully-automated cars, however, is likely to be long and beset with concerns about legislation, safety, and liability, to name a few. And the transition to the new technology is likely to be uneven, with a wide variety of driven and driverless vehicles coexisting on the nation’s highways for years to come.

Is that a cell phone in your pocket?

Myra Blanco, director of the Virginia Tech Transportation Institute’s Center for Automated Vehicle Systems, likes to compare automated cars (a term she prefers to “driverless”) with cell phones.

What would have happened, she asked, if Motorola engineers working on the first handheld mobile phone more than 40 years ago had halted the project because what they had was as cumbersome as a brick and performed only a fraction of the functions common in today’s cell phones?

“Think about the cell-phone industry and how quickly things have progressed,” Blanco said. “Can you imagine if we had said to the cellphone industry, ‘don’t develop this because it can’t take pictures?’”

Sure, she says, anyone can come up with dozens of potential pitfalls for automated cars: Will we need widespread connectivity to keep them on the road? What happens if a flash flood washes out a road an automated car is about to take? And what happens if lightning literally strikes and fries the car’s autopilot systems?

“There are problems and solutions we don’t even know will exist. Our questions now are more advanced than the technology,” Blanco said.

People will have to develop counter-measures to address problems that arise, she said. Some of these will include built-in backup systems, or redundancies, which are already commonly engineered into aircraft, for example.

To get around, an automated car would rely primarily on high-definition maps and onboard cameras that recognize the surrounding terrain. A third component could perhaps help it spot that washed-out roadway. And then there’s always the human factor. A car owner could simply decide against venturing out when torrential rains are in the forecast, she said.

Drivers take a back seat

In just five years, cars will likely be able to recognize everything around them, be it another car, a stop sign, or a pedestrian, Blanco said. On the other hand, she said we’re probably still two to three decades away from being able to summon a car, assign it a destination, and sit back and relax.

Nevertheless, next year will mark the start of “rapid growth” in advanced driver assistance systems, analysts at Goldman Sachs said in a recent note.

The market for these systems’ core features, which use radars, lidars (a type of light-based remote sensor), ultrasonic sensors, and cameras, is expected to balloon to $10 billion in 2020 from just $2 billion in 2013.

Goldman’s top investment picks among those making driver-assistance systems include Israel’s Mobileye NV US:MBLY, a leader in software algorithms, Japan’s Denso Corp., partly owned by Toyota Motor Co. 7203, +0.24% , and car-parts makers Continental AG CON, -4.80% of Germany and Delphi Automotive Plc. DLPH, -3.28% in the U.S.

Some car makers are focusing mostly on stop-and-start city driving, while others are concentrating on developing automated cars for the open road. The so-called new entrants, such as Google and Apple Inc. AAPL, -1.45% , are focusing on autonomous vehicles to operate in limited areas at first.

And it’s entirely possible all these vehicles will be sharing the road in a few years. Cars requiring some level of human intervention likely will coexist with fully autonomous systems, such as pod-like, low-speed vehicles that could shuttle people in well-defined areas such as a downtown commercial district, campus, or military base, or small driverless trucks making deliveries along specific routes.

While tech companies claim a very short timeline is needed to develop automated cars, the auto industry is being a bit more conservative, Blanco said.

SAE International, an association of engineers, has defined six levels of automation, ranging from zero, or no automation, to five, or a fully automated car that needs little input from a driver.

The cars equipped with driver assistance today are usually classified SAE level 2, which means some driving tasks are partially automated.

The gap between level 2 and level 3 is a big one, however. At level 3, driver-assistance systems can not only steer and control a car’s speed but also monitor road conditions and the car’s surroundings.

At level 3, the human driver really starts taking a back seat, although no naps or texting would be allowed: drivers are expected to remain alert and intervene as directed by the system. Here’s how the SAE engineers have defined levels of automation:

Going to a car rodeo?

Inside a level 5 car, naps would be OK, which is either bliss or misery depending on how much one loathes or loves to drive.

Driver behavior, however, will likely need to change to reflect changed circumstances, according to John O’Dell, a senior editor at Edmunds.com.

O’Dell, who faces a 54-mile daily commute in Los Angeles, would like nothing more than a car that whisks him effortlessly to work. “On Saturdays, however, I may want to drive [that same car]”, he said.

Then there’s the problem of sharing the road with so-called legacy cars. O'Dell estimates it takes about 14 years in the U.S. to fully refresh the fleet of existing vehicles, and that’s not counting cars that have earned “classic” status among aficionados and are likely to be trotted out indefinitely.

Driving could become something most of us would only do for pleasure, such as cruising the back roads, and something we do or watch at special car shows or events, not unlike the way most of us now connect with horses.

Safer cars

Meanwhile, driver-assistance features are making cars safer, reducing crashes and functioning at much higher speeds, said David Aylor, a senior research engineer with the Insurance Institute for Highway Safety.

Initially available only on high-end models, these systems have gradually become more widespread and could be standard in budget vehicles as soon as five years from now, he said.

In 2010, according to Edmunds.com, a little over 70 models, mostly luxury brands such as Audi and Bentley, sported adaptive cruise control, a powerful but relatively simple driver-assistance system that automatically adjusts speed to maintain a safe distance to traffic ahead.

This year, nearly 170 models have adaptive cruise control, including Ford’s family sedans and Toyota’s minivans.

The new driver ed

All told, most of the technology for autonomous cars already exists, said Edmunds.com’s O'Dell. “Maybe there are some issues around hardware size and refinements to software, but it’s largely here,” he said.

What still needs a lot more work, however, are the social and legal aspects surrounding autonomous driving, O’Dell said. Drivers need to understand that they’ll still have to pay attention to the road for years to come, even as systems improve and cars become more automated, he said.

Jets can practically land themselves and they can definitely cruise at high altitude, “yet pilots still go through hundreds if not thousands of hours of training” to remain alert and respond to any situation at any moment, O'Dell said. “Massive new training for drivers will be needed,” he said.

A Tesla Model S instrument cluster showing cruise control and, to the left, the desired distance between cars.

In 10 years, it’s unlikely that private cars and trucks will have reached the “no hands” level of automation, but autonomous vehicles, such as pod-like systems and small delivery trucks, will likely be around. That will raises questions about their coexistence with fully autonomous vehicles as well as the old zero-automation vehicles, which will remain on the roads for years to come.

Another issue linked to driver education is determining who is responsible when an automated car crashes. Is it the driver, the owner of the car, or the maker of the radar that might have failed?

In the not-so-distant future, cars will likely carry their own “black boxes,” O'Dell said. “They are going to be able to tell everything” about accidents they been involved in.

Experts also talk about changes in the insurance industry, with car makers perhaps managing a master liability policy and passing down the cost of such a system by bundling it into one’s car payments, he said.

Bryant Walker Smith, an assistant professor of law at the University of South Carolina who has focused on self-driving vehicles, said in a recent blog that determining who’s responsible for a crash in an autonomous car is likely to be similar to determining who’s responsible for a crash today: “It depends,” he wrote.

Accidents often involve many parties, and accidents with automated cars will likely be little different: the owner could be held responsible for failing to properly maintain the vehicle; a driver could be taken to task for improper use of the car’s automated features, a manufacturer could be liable for failing to warn the user, and so on, he wrote.

Engineers, government officials, scholars and lawyers are all wrestling with the many questions surrounding autonomous driving. Only a few things are clear, said Virginia Tech’s Blanco: “We will surpass the limits of our imagination in 30 years,” she said. “This is the beginning of an amazing future.”