Why keep your hands on the wheel?
Right now on a busy stretch of highway somewhere, a driver is gazing out of the window, hands on his lap, feet off the pedals.
Such driver-assisted motoring, a midpoint on the journey to fully self-driving cars, uses radar and cameras to help a car steer, brake, and even change lanes.
But as such features begin to emerge in less expensive cars, a vexing question looms: Automakers from Tesla to Nissan all caution that their tech must be monitored, but can humans be trusted to do so?
"These systems are designed not only for ideal environments like good weather and clear lane markings, but also for rational behaviour, and humans are predictably irrational," says Bryan Reimer, a research scientist at the Massachusetts Institute of Technology who specialises in self-driving tech.
"The question is, does the automation work so well and require so little of you that, in essence, a new safety problem is created while solving for another?" Reimer asks.
Spotlighting such concerns are two recent deadly crashes. A month ago, a Uber self-driving car killed a pedestrian in Arizona despite having a driver at the wheel who was supposed to monitor the vehicle. The incident has ignited debate over whether testing autonomous cars in public is appropriate.
And a week later, a Tesla Model X in Autopilot mode slammed into a concrete highway divider in Mountain View, California, killing driver Walter Huang. Huang's family is suing Tesla, but the company says that Huang repeatedly ignored prompts to retake control of the wheel.
While litigators skirmish over assigning blame, the death has caused some experts to wonder if such features are encouraging drivers to take more risks than the technology can handle.
Nearly a dozen automakers offer variations of this tech, from Mercedes-Benz's Driver Assistance Package on its $90,000-and-up S Class sedan to Nissan's recently introduced ProPilot Assist that is now available on the $23,000-and-up Altima.
Dubbed Level 2 systems by the Society of Automotive Engineers, with Level 1 being cruise control and Level 5 being autonomous mode, these four-figure technology packages typically require drivers to check in with the system through frequent steering wheel inputs.
While often quite competent, the tech is far from flawless.
"In every system I've tried, I've been able to discern situations where (the car) got confused such as when lane lines drift away at an on-ramp," says Karl Brauer, executive publisher of Cox Automotive.
"If you have this tech, realise there are common circumstances even the best system can't handle," he says. "If you can't watch out for that, you shouldn't have it."
Among the most innovative and ambitious driver-assist systems on the market is from General Motors, whose Super Cruise package lets drivers take hands off the wheel and feet off the pedals as the vehicle steers itself along any highway GM has mapped into the car's computer brain.
Dubbed by GM the "first hands-free driving technology for the highway", Super Cruise uses its tech to create a virtual centre line in the lane, which the car follows, and its mapped knowledge of the road's bends and elevation changes keeps the vehicle at a steady speed.
The system will hassle you if you're not looking straight ahead. Using a driver-facing infrared camera that monitors head position, Super Cruise launches into a variety of warnings, ranging from chimes to shaking your seat, before bringing the car to a stop.
"(We) require the driver to be ready to take control of the vehicle at all times during operation," says Daryl Wilson, lead development engineer on Super Cruise, which bowed on the flagship Cadillac CT6 sedan.
Tech enables the risk takers
Yet despite the litany of warnings in manuals and in-car visual and auditory cautions, humans don't always listen to their better angels.
Working against prudence is everything from nomenclature (Tesla's Autopilot name even gets dinged by fans of the system) to advertising (Mercedes in 2016 had to pull its ad for the new E-Class, which boasted that it was a "self-driving car from a very self-driven company").
Online videos feature drivers showing off what they can do while their car motors along on its own, with some hopping into the rear seats while ignoring visual and audio prompts to resume control.
Some drivers are even willing to pay for help tuning out such warnings. For $179, you can buy an aftermarket plug-in device called Autopilot Buddy that promises to "extend the use of Autosteer on Tesla vehicles by reducing the check-in 'nag' warnings".
Technology can potentially help with the modern-day driving scourge that is distracted driving, a phenomenon that arrived with the cell phone and which was exacerbated by the smartphone. Last year, 40,000 Americans died in traffic accidents, up six per cent from 2015.
But for every vehicle that saves the day by perhaps braking on its own before the driver sees the threat, there are other instances in which drivers get too comfortable that their vehicles have the situation in hand.
A recent Esurance poll found that 25 per cent of buyers of driver-assist tech disabled at least one feature since buying the car, and 29 per cent said that they found the in-car warnings a distraction.
That concern with 'over-trust' was a constant source of discussion when Nissan was developing its ProPilot Assist system, said Ryan Rumberger, senior project manager for Nissan's autonomous driving performance tests.
In the end, the company went with a system that requires a driver to keep his hands on the wheel.
"You need to be ready to deal with people cutting in, people swerving. This is not a self-driving system," Rumberger says. "You see all these recent accidents, and it definitely makes us look hard at what we built to make sure it doesn't happen with our products."
Tesla Autopilot under scrutiny
Tesla has been in a particularly harsh spotlight for fatalities associated with Autopilot. Despite the requisite cautions about the limits of the tech, CEO Elon Musk did not complain when users posted videos that touted the system's ability to cruise along unminded, often with the driver in the back seat.
Actress Talulah Riley, Musk's ex-wife, even posted a video in 2016 driving on a highway with her hands off the wheel. Tesla's stance remains that it "requires drivers to remain engaged and aware when Autosteer is enabled. Drivers must keep their hands on the steering wheel."
"In the original call (with analysts) discussing Autopilot, Musk talked about you being able to go from Los Angeles to San Francisco without touching the wheel, but in reality that the system is just adaptive cruise control with smooth lane-keeping assist," Gartner analyst Mike Ramsey says.
Ramsey says that the inherent danger of driver-assist features is that the better and more consistently they work as advertised, the easier it is for humans to abdicate their responsibility at the wheel.
"Tesla tried hard to insist the system is hands on while delivering a system that works well hands off," he says. "It's like giving kids chocolate and telling them they can only smell it."
Tesla enthusiast and video blogger, Ben Sullins says when used correctly, Autopilot can quickly sway newcomers to the brand.
"If someone's new to Autopilot, there's certainly a temptation after using it to have blind faith in how good it really can be, maybe tied partly to blind faith in Elon and his aura," says data scientist Sullins, founder of the Teslanomics website and who owns a Model S and Model 3. "But use it for a week, and you come to terms with what works and what doesn't."
Zac Cataldo found that Autopilot not only worked just fine on his 25-state, 8,000-mile trek in a Model X, but often, it made logging long highway miles a breeze given that all he had to do was monitor the car.
"When Autopilot is doing what it's designed to do, mainly on the open road, it's very good," says Cataldo, host of YouTube channel NowYouKnow.
But Cataldo adds that Tesla owners tend to come in two Autopilot camps.
"I've met drivers who swear by it, and others who say they never use it and would never trust it," he says. "Personally, I think of my Tesla on Autopilot as a 16-year-old driver, where I'm ready to take over because it doesn't know as much as I do. But maybe in a few months, it'll drive more like a 20-year-old."
Tesla provided a long email outlining the many ways it tells owners to stay engaged when using Autopilot. The system is constantly being tweaked by its engineers, who push out over-the-air updates.
The company said in a blog post that the Mountain View crash happened at a spot that since the beginning of the year has been passed uneventfully 20,000 times by Teslas using Autopilot.
The Mountain View scenario is an echo of another Tesla crash in 2016 when a Florida man was killed when his Model S hit a truck that cut across his lane. National Transportation Safety Board investigators concluded that he also ignored warnings from the vehicle but added that the system gave the driver "far too much leeway" to do something other than drive.
The best advice for anyone in the market for driver-assist features is to spend time trying them out at the dealership, says Sam Abuelsamid, a former automotive engineer turned auto tech analyst for Navigant.
"Humans usually make very bad supervisors for automated equipment," he says. "We get used to the machines working well, so switching modes rapidly to human control can be tough. And on the road, things can happen very quickly."