LAS VEGAS – The Toyota Research Institute (TRI) pumped the brakes on fully autonomous cars at CES 2017. TRI CEO Gill Pratt said at the company’s press conference that the entire industry is “not even close” to launching fully autonomous Level 5 cars.

He added that it “will take decades to have a significant portion of US cars operate at Level 4 autonomy or higher.”

According to SAE International, Level 5 autonomy means no steering wheel, no brakes, and no human driver required. Pratt’s remarks certainly aren’t in line with what most other automotive companies have said. Recently, for example, Ford said it would mass-produce Level 5 vehicles by 2021, and Tesla said its Level 5 cars will be ready in 2018.

“Level 4 cars will be on the road in 2020 operating in certain environments,” said Pratt. He added that “it’s going to take many years of machine learning and many more miles than anyone has logged to achieve Level 5 autonomy.”

Pratt said part of the problem is humans have historically had little to no tolerance for injuries and deaths caused by machines. Pratt said TRI isn’t content with self-driving cars being as safe as humans. Being twice as safe isn’t acceptable either, he said.

“What if the machine was twice as safe as a human-driven car and 17,500 lives were lost in the US every year? Would we accept such autonomy?”

Level 3 cars, which must give the driver sufficient warning before it hands off control when something goes awry, also present a major challenge. Some drivers will trust the technology too much and fully engage in other tasks. This will cause them to be unprepared to take the wheel when needed, and other times there isn’t enough time for the hand-off to take place.

“Considerable research shows that the longer a driver is disengaged from the task of driving, the longer it takes to re-orient,” Pratt said.

A car driving 65 MPH travels around 100 feet every second, Pratt said. To give a disengaged driver 15 seconds of warning in a car traveling at that speed, the car must spot trouble about 1500 feet away. That’s extremely hard to guarantee, and unlikely to be achieved soon.

This led Pratt to talk about Level 2 cars, which he said are the most controversial type of autonomous car at the moment. The problem here is that the hand-off may occur at any time with only a second or two of warning. This means the human driver must be able to react, mentally and physically at a moment’s notice.

Pratt discussed all this as Toyota introduced its Concept-i car that uses an AI system called Yui (pronounced you-EE) that is designed to engage with drivers and keep them aware of their surroundings. For example, Yui could simply engage the passenger in a simple conversation to make sure he/she is paying attention. Yui can also use light, sound, and even touch throughout the car’s cabin to relay critical information to the driver.

“At TRI, we think that Yui might not only be a way to engage with human beings and create useful advice to the driver, we think it might also be a way to modulate and maintain a driver’s situational awareness using mild secondary tasks to promote safety,” says Pratt.