EVEN before Tesla revealed that a fatal accident had occurred while one of its cars was in semiautonomous driving mode, a debate was well underway between researchers and engineers: Is it possible to get a driver to safely take back control of a car once the vehicle has started driving itself?

The question is relevant not only for cars of the future but also for ones already on the road.

While the Tesla Model S has been getting all the attention in the last week, the fact is that many cars, including models from BMW, Mercedes-Benz and Volvo, now have systems that use a combination of adaptive cruise control, lane-keeping and automatic braking to enable drivers to briefly take their hands off the wheel and their eyes off the road.

Some Tesla drivers have reveled in making videos of themselves using the Autopilot feature. But the more conventional automakers have designed their systems to take control of the car for only a few seconds at a time; the driver must be ready to resume command at any time.