Level 3 presents a complicated, ‘mushy middle’ in automated driving

The uncertainty could breed problems for drivers.

“I fear that drivers may not read this fine print and find themselves in a position where they honestly believe they are now allowed to take their eyes off the road and pick up their phone or other devices,” Funkhouser said.

The question of what human drivers could — or should — do with their time comes as lawmakers are growing more concerned about driver distractions. Answers could vary by state.

Michigan enacted legislation this month that makes it illegal for motorists to physically send or receive phone calls or text messages, or access, read or post to a social networking site while driving. A more stringent New York law prohibits drivers from removing their hands from the wheel. But it does allow for voice commands and hands-free modes.

“Lawmakers are fighting tooth and nail to drive attention spans and more engaged driving,” said Jennifer Dukarski, an attorney who specializes in vehicle safety and emerging technologies at Butzel law firm in Ann Arbor, Mich. As for Level 3, “the public is going to perceive this as less-engaged driving,” she said.

Even though motorists may be asked to take over, there’s no expectation in Level 3 that they will pay attention until that point, said Koopman, who helped write the SAE levels standard, which is codified in California’s automated driving statutes.

“If there’s a firetruck parked in the middle of the road or the traffic light is red, you — the human — have no obligation whatsoever to notice that,” he said.

But NHTSA says something slightly different for Level 3. Humans can “disengage from the driving tasks under limited circumstances,” the agency’s spokesperson said. Human drivers “must be ready at all times to respond to any cues to intervene.”

Theoretically, human drivers would have a defined period of time between a prompt to retake control and actually doing so. But there are no standards on what the duration of that period should look like.

Mercedes-Benz declined to say how it will notify drivers to retake control and how long they would have to remain in control.

It took drivers an average of 6.1 seconds to return their visual focus to the road following a system-initiated request, according to a study published in March by Reimer and his MIT colleagues.

Those results came while examining Level 2 driver-assist systems, with which human drivers always bear responsibility. Reimer is concerned that Level 3 systems would lead to even longer times needed for motorists to regain situational awareness. It’s why he deems systems where drivers are theoretically allowed to divert their attention from traffic as non-starters.

“If you have to be ready at all points in time to take control, that means you can’t pay zero attention to the road,” he said.

Should motorists fail to respond to takeover prompts, the issues surrounding Level 3 deployments grow more vexing.

Mercedes-Benz said if the driver fails to retake control “after increasingly urgent prompting and expiration of the takeover time,” the system would bring the vehicle to a standstill and activate its hazard warning lights.

The company declined to answer questions on how those prompts work and whether such a standstill would occur within the vehicle’s lane of travel or if a car could navigate to the shoulder. In an interpretation of federal safety standards issued in 2016 involving automated driving systems, NHTSA said that vehicles coming to a stop in lanes of travel could constitute a safety defect.