This is the most dangerous time for drivers, expert says

With partially autonomous cars already on U.S. roadways, this could be the most dangerous time for drivers, the head of Duke University Robotics said Tuesday.

"To get to fully autonomous car world, we have to get through this scary period that we're in which is the partially autonomous car," Mary Cummings said in an interview with CNBC's " Power Lunch ."

"The expectation is the driver will intervene occasionally or maybe even rarely and that is the worst time to expect a human to intervene."

Automakers and tech companies are all competing to get driverless cars onto the market , with some already putting semi-autonomous technology into their current vehicles.

That technology has been in the spotlight since a fatal Tesla Model S crash in May involving Autopilot . U.S. auto safety regulators are now investigating the accident.

Richard Wallace, research director at the Center for Automotive Research, agrees that this is a risky time for the industry.

And since people keep their cars a long time, once driverless cars become available there will be a long transition time of mixed traffic, he said.

"That's the scariest evolutionary period," he told "Power Lunch."

Right now, however, U.S. Transportation Secretary Anthony Foxx sees value in the systems being out there on the roads.

"There's an opportunity with the data that these systems develop to have shared knowledge between systems, just like we do with the FAA, where an individual vehicle experiences an avoidance situation they can teach other vehicles to do the same thing in similar situations," he said in an interview with CNBC from the Automated Vehicles Symposium in San Francisco on Tuesday.

The goal behind driverless, or fully autonomous, cars is to cut down on fatal crashes, with the thought that computers make better drivers than humans.

Despite her misgivings about the current situation, Cummings is a big believer in driverless cars once the right technology is in place.

"Once we get the fully autonomous car that can really drive by itself and has no expectation that the human will intervene, life will be great. But we're not there yet," she said.

And Wallace believes that once the technology is available, the buyers will come.

"There's a lot of consumer evidence out there people are willing to pay for this because they think it's going to help them save lives. We face close to 40,000 traffic fatalities a year in the U.S.," he said.

Wallace isn't even anticipating the cost will be extremely high, noting it could add another $1,000 or $2,000 to the price of the car.

For one, prices have fallen dramatically on sensor sets.

"Software is obviously critical here. Replacing your eyes and your ears — that's the easy part. Replacing your brain, that's the hard part," Wallace said.

— CNBC's Phil LeBeau contributed to this report.