Cars are getting better at driving themselves, but you still can't sit back and nap

If you're taking a lot of road trips this holiday season, maybe you've wished your car could just drive itself to Grandma's house.

The auto industry has been working on autonomous driving for years. And companies like Waymo and Cruise are testing fully autonomous driving — in some cities, you can already hop in a driverless taxi.

But if you want a genuinely self-driving car of your own, you're out of luck.

Yes, vehicles are getting better at controlling their own steering and acceleration in more situations.

But despite all the fancy names being used by automakers, the technology is still nowhere near the point where the car can handle all the driving while you nap — a distinction drivers must keep in mind.

"There are exactly zero self-driving cars available for purchase, anywhere in the world today, from any manufacturer," says Sam Abuelsamid, principal analyst at Guidehouse Insights.

Hands off the wheel, but eyes on the road

Take General Motors' Super Cruise. It's one of a slew of confusingly named "advanced driver-assistance systems" that allow cars to control their own steering and/or acceleration.

And it's one of just a few systems that allow a driver to actually — safely — remove their hands from the wheel on the road. For now, the feature is only available on some highways; it relies on a combination of GPS, high-precision maps, cameras and radar.

When it's working, the vehicle can automatically control its speed and steering without the driver having to touch a pedal or the steering wheel. That might seem pretty close to the dream of a car that can do the driving for you.

But the technology doesn't work 100% of the time — and it doesn't pretend to.

When a vehicle with Super Cruise encounters a situation it finds confusing, like a construction zone or a stretch of highway where its map is missing data, it will hand control back to the driver.

The car signals that it needs assistance by flashing red lights on the steering wheel, and on some vehicles, through vibrations in the driver's seat.

And if something unexpected happens on the roadway, the driver is supposed to be ready to seize control in an instant.

Because the car needs help some of the time, the driver has to pay attention all of the time.

"The human is always responsible for driving, even when you're hands-free," says Ron Arnesen, executive chief engineer for automated driving and active safety programs at GM.

GM doesn't assume people will do the responsible thing and pay attention.

There's a camera embedded in the steering column that tracks the driver's eyes — even behind sunglasses — to make sure they stay on the road. Should the driver's gaze wander, the vehicle makes progressively more alarmed buzzes, flashes and alarms, and eventually refuses to drive itself any more.

It's an essential safety feature, Arnesen says, because GM knows that Super Cruise will not be able to handle all road situations.

"If you're always paying attention," he says, "you can take over within a matter of a split second if you need to."

Even "Full Self-Driving" requires human oversight

Tesla, more than any other automaker, has heavily marketed the idea of a car that can genuinely drive itself.

Its "Autopilot" driver-assistance technology is a major selling point for the vehicles.

And a small number of drivers are now getting to test the long-promised "Full Self-Driving" software, which allows a Tesla to steer itself on ordinary city roads — handling turns, waiting at stoplights and responding appropriately to the sometimes-unpredictable behavior of other vehicles and pedestrians.

Hypothetically.

For now, Tesla's technology still requires a human to have their hands on the wheel and eyes on the road, despite being called "full self-driving."

"I like to keep my foot, like, hovering in between the gas and the brakes," says Victoria Scruggs, a Tesla owner who is part of the beta test. "You really don't know what it's going to do sometimes."

In a recent test drive with Scruggs, her Model 3 drove perfectly reasonably through some intersections. At others, it hesitated, or moved with strange jerkiness, or shut off mid-route and put Scruggs back in charge.

Scruggs says a previous version of the software swerved so aggressively into the wrong lane that it actually hurt her wrist.

In general, she says, her Tesla can drive itself very well on highways. It can do OK going straight on city streets, she adds.

"But when you throw turns into the mix, it's a little bit iffy," she says.

On city streets, the software makes driving more stressful, not less, she says. And as a Tesla beta tester, she uses it not to make her life easier, but to collect more data to help the company make the software better.

Tesla's marketing and rollout of this technology is controversial.

Tesla's more limited Autopilot technology, which only handles simple driving tasks and is less erratic, has been involved in deadly crashes, and multiple incidents in which it didn't seem to recognize emergency vehicles.

Safety advocates have expressed concern that Tesla drivers may be relying too heavily on Autopilot, assuming the technology will function better than it will.

They've also criticized "Autopilot" and "Full Self-Driving" as dangerously misleading names, and have raised concerns about Tesla testing experimental software on public roads.

Tesla, which has been criticized for exaggerating the capabilities of its software, did include a pretty blunt warning for drivers testing the "full self-driving" features. It cautions that it could do "the wrong thing at the worst time."

The better cars get, the harder they are to supervise

While no personal vehicles are 100% self-driving, the amount of driving these systems can handle on their own is impressive, compared to what was available on the market just a few years ago.

And it's not just pricey, cutting-edge Cadillacs and Teslas that have seen significant progress in this area.

Kelly Funkhouser, who runs automated vehicle testing for Consumer Reports, says car shoppers might be surprised to learn just how many new cars can do some driving for you.

More than 50% of new vehicle models can control speed and/or steering in highway driving situations, she says – even if they can't navigate for you from start to finish, handle highway lane changes or allow you to (hypothetically) paint your nails on the freeway.

High-tech driver assistance features do make driving — especially long highway hauls — much easier. They certainly make it more pleasant. And in some cases, like when cars automatically hit the brakes to avoid an accident, they can have clear safety benefits.

Still, these vehicles all require close human oversight to work safely.

And the smarter our cars get, the more challenging that becomes. Funkhouser says these driver assistance functions make driving "even more boring," and that worries her.

"It's human nature, really, to just kind of want to zone out and find something exciting to do other than watch the car drive," Funkhouser says. "It's just like watching paint dry, right?"

"That's what worries us most about these systems," she says. "As they become more competent, then it's easier for drivers to kind of want to check out and find something else to do."

In other words, you still need to keep your eyes on the road for that long drive to Grandma's house — no matter how boring it gets.