CAMBRIDGE, Mass. -- While much of the media attention around autonomous vehicle technology has been focused on fully self-driving cars, consumers shouldn't expect cars to act like chauffeurs any time soon.

The vast majority of mainstream vehicles adopting autonomous driving features will be controlled by advanced driver assistance systems (ADAS) or "guardian angels" that learn over time, Gil Pratt, CEO Toyota Research Institute, told reporters and analysts last week.

Speaking at the New England Motor Press Association Technology Conference at MIT, Pratt said that 30,000 motor vehicle fatalities occur in the U.S. each year. That number may seem high, but as a whole, U.S. drivers are excellent at avoiding crashes.

So, instead of taking the wheel from drivers' hands, as a fully autonomous vehicle would do, auto makers are more focused on assisting drivers for years to come.

"Despite the fact that there are 30,000 fatalities in the U.S. per year, driving in the U.S. is extraordinarily safe per mile," Pratt said. "It turns out we drive a lot in the U.S. So if you work out fatalities per mile, there's one fatality per 100 million miles [driven] in the U.S."

According to a recent poll, the overwhelming majority of U.S. drivers don't want fully autonomous vehicles. The online survey conducted by the University of Michigan revealed that 37.2% of drivers were "very concerned" about riding in a completely self-driving vehicle, while 66.6% were "very or moderately concerned."

The most frequent preference by those surveyed was for no self-driving technology (45.8%), followed by partially self-driving (38.7%), with completely self-driving being preferred by only 15.5% of respondents.

Earlier this year, Toyota announced a six-person tech team to head up its new Toyota Research Institute (TRI), with the objective of making cars safer and ultimately incapable of crashing.

Pratt referred to fully autonomous driving technology, like the kind Google is testing at various regions around the country, as artificially intelligent chauffeurs.

"If you love to drive, the idea of a chauffeur is not fun," Pratt said. "Driver skills are ignored with a chauffeur; with guardian angel technology, you're augmenting human driving skills."

Guardian angel technology would be able to learn over time, even picking up on user's driving habits so that it could spot trends that could lead to accidents and advise the driver to make corrections that would prevent a crash from occurring.

Pratt pointed out that road conditions, sunlight, even a box suddenly falling from the truck in front of you could thwart a fully autonomous vehicle. Simply put, self-driving technology is still far from perfect.

But fully autonomous driving technology needs to be perfect before it can be rolled out en masse, said Pratt, a former MIT professor who, prior to joining Toyota, headed the Robotics Challenge at the U.S. military's Defense Advanced Research Projects Agency (DARPA).

"Toyota's [entire fleet of vehicles] drives 1 trillion miles per year or about 10,000 miles per car," Pratt said. "How many accidents caused by some error of the machine, let's say software, will the public put up with? The answer is almost none."

The standard that the TRI is trying to beat with its guardian angel ADAS technology is that of humans' natural ability to avoid crashes, which is a high standard. Most important, he said, is to avoid adding any technology that might cause a crash instead of preventing one.

Some of the ADAS technology will be passive, as in today's warning systems that beep or vibrate the steering wheel to alert drivers of hazards, while others will be active, such as self-braking cars.

The U.S. Department of Transportation's National Highway Traffic Safety Administration (NHTSA) and the Insurance Institute for Highway Safety (IIHS) announced earlier this year that 20 automakers have pledged to make automatic emergency braking (AEB) standard on their cars by 2022.

A lot of the discussion among automakers and within their R&D organizations involved how much control the car should have.

For example, Pratt said, your car may someday warn you several times about a particularly dangerous driving habit you have before taking control of the wheel.

Autonomous driving capabilities are measured on a government scale of zero to four, with zero being no automation, and four being fully automated.

The focus of most of the discussion among car makers today is how far up the scale they should go and how quickly, Pratt said.

"There's a lot of discussion in the industry whether we go incrementally up the scale or whether we jump," he said. "The chauffeur and guardian angel are built out of the same technologies. I actually believe they are complementary to each other."