Americans prefer the option to drive, even in a world where cars can drive themselves.

A new study from Kelley Blue Book shows how Americans' affinity for driving could slow the adoption of driverless vehicle technology in the United States. Rather than fully autonomous vehicles, Americans prefer cars equipped with self-driving capabilities, but with the capability to butt-in as desired.

That's a striking conclusion for those preparing for a fully driverless future. Lyft recently expressed its belief that private vehicle ownership would be phased out in major cities by 2025, largely because of self-driving cars.

New research from Kelley Blue Book shows how dramatically self-driving cars could alter the landscape of car ownership by 2020. By then, 6 in 10 consumers will be interested in buying cars that are at least partially autonomous -- ranging from "autopilot"-equipped Teslas that garner so much amazement today, to fully autonomous cars with no human drivers.

But the findings also show that people are wary of such technology. Among the conclusions: More than half of respondents preferred to have full control of their vehicles, even if it means roads are less safe. Respondents see full autonomy mostly as a service for mobility-limited drivers, such as senior citizens, and a mobility option for outings involving alcohol. And more than 6 in 10 consumers don't think they'll live to see a world where all vehicles are self-driving.

Experts said it's possible developing countries could move toward full vehicle autonomy faster than the United States.

"When you think about the infrastructure that's being created in places like China and India, they can actually plan and build for autonomous vehicles, where we are retrofitting everything here in the states," said Rebecca Lindland, senior director of commercial insights for Kelley Blue Book. "In the U.S., we are a driving culture. Everybody has a car . . .whereas in some of these other places, if you only know ridesharing, if you never own a car and you only rideshare, that's going to be perfectly normal for you."

The respondents most comfortable with self-driving cars had some exposure to semi-autonomous features -- such as adaptive cruise control, lane correction and assisted parallel parking. They were the most likely adopters of self-driving cars; they found fully driverless cars "significantly more appealing" than their standard vehicle brethren, the research showed. But those consumers made up only 12 percent of current vehicle owners.

"Familiarity here is breeding adoption, whereas unfamiliarity can breed some contempt," Lindland said.

The survey determined that self-driving cars with the option for human control are the "sweet spot" when it comes to vehicle autonomy.

"There are times that it is fun to drive a car -- out in the country where you can stop or slow down to look at things. But for a long trip, the full autonomy would be great," read one survey response.

Kelley Blue Book, the car valuation and research firm, commissioned the study in May; Market research firm Vital Findings surveyed 2,264 respondents ranging from 12 to 64 years old. The youngest respondents felt they were the most educated about driverless technology, while baby boomers felt they knew the least.

Full autonomy was most appealing to the youngest generation surveyed -- Generation Z, consisting of respondents from 12 to 15 years old. Forty-eight percent said they were comfortable being driven without their control, proving "pre-driving Young Gen Z don't crave vehicle control like their cohorts," according to the study. Members of that generation said they would like their first vehicles to be either autonomous with the human driver option, or fully autonomous.

From there, older millennials (those with purchasing power) were the most comfortable with fully self-driving cars.

Unsurprisingly, ride-hailing users were more likely to be comfortable being ferried in self-driving vehicles than those who don't use services such as taxis, Uber and Lyft. As for the driverless future Lyft predicted? Lindland expressed skepticism, citing the survey's findings.

"The idea that people are going to just completely abandon personal vehicle ownership, there is really very little indication for that and there's absolutely none in this study when you think the general attitudes even towards autonomous vehicles is not 100 percent," she said.

She predicted that self-driving cars would go through a break-in and adjustment phase, much like cellphones during their initial rollout, as consumers decide what is best to fit their needs.

"We're gonna go through these stages of up and down. You think about the size of the phone -- first they were huge then they got really really small and then they got bigger and then they kinda got too bigger then they got a little too small. So we're gonna see these sticks and starts and back and forths as we develop and find what's suitable for everybody."