We humans are easily distracted by our games, phones and mates. And automotive engineers, computer interaction designers and, yes, lawyers, wonder if the self-driving cars they are working on will ever really be able to count on us in an emergency.

Engineers say they believe that cars will be intelligent enough to do all the driving, somewhere between five years and a decade from now, depending on whom you ask. But until then, what passes for autonomous driving will be a delicate ballet between human and machine: Humans may be required to take the wheel at a moment’s notice when the computer can’t decide what to do.

To outline a development path to complete autonomy, the automotive industry has established five levels of human-to-machine control, ranging from manual driving — Level 0 — up through complete autonomy, Level 6. In the middle, Level 3 is an approach in which the artificial intelligence driving the car may ask humans to take over in an emergency.

But many automotive technologists are skeptical that the so-called handoff from machine to human can be counted on, because of the challenge of quickly bringing a distracted human back into control of a rapidly moving vehicle.

“Do you really want last-minute handoffs?” said Stefan Heck, chief executive of Nauto, a start-up based in Palo Alto, Calif., that has developed a system that simultaneously observes both the driver and the outside environment and provides alerts and safety information. “There is a really good debate going on over whether it will be possible to solve the handoff problem.”