Many people dream of one day riding down the highway, feet on the dashboard, newspaper in hand, while their vehicle drives them to work. No more time spent sitting idle behind a steering wheel; no more stop-and-go traffic; improved safety, and better fuel economy, too.

Automated driving technology continues to improve. Experts now say they there could be millions of autonomous cars on the road in the next two decades. Big names from the tech and automotive industries are pouring hundreds of millions of dollars into self-driving vehicles, including Google, Uber, Tesla, Audi, BMW, Ford and others.

Just last week, Google received a patent for a protocol that allows self-driving cars to respond to unexpected events when they have to deviate from their preplanned routes -- like how to plot a new path around a herd of cows.

But there might be one thing proponents of self-driving cars and their prospective users haven’t considered yet: motion sickness.

Motion sickness is expected to be more prevalent among users of autonomous vehicles than of conventional ones, according to a new study by the University of Michigan Transportation Research Institute (UMTRI). That’s because the three main factors that trigger nausea -- conflict between the inner ear and visual inputs, inability to anticipate the direction of motion, and lack of control over the direction of motion -- are all exacerbated in self-driving cars.

Whether or not passengers experience motion sickness is largely determined by the type of activity they’re engaged in in the vehicle. The UMTRI report calculated the expected frequency and severity of motion sickness in autonomous vehicles, based on a survey of what more than 3,200 adults in six different countries are likely to do in a fully autonomous car.

Results showed that 6 percent to 10 percent of American adults riding in fully autonomous vehicles are anticipated to “often, usually, or always” experience some level of motion sickness. Another 6 percent to 12 percent of American adults are anticipated to experience “moderate or severe” motion sickness at some point in time.

Indians are expected to suffer the most, with up to 17 percent of adults experiencing moderate or severe motion sickness during a typical trip. (Again, results are based entirely on the activities which individuals of different nationalities said they would engage in while riding in an autonomous car.)

Michael Sivak, UMTRI research professor and author of the report, recommended several design features that could help reduce nausea, such as large windows, displays intended to keep a passenger's gaze facing forward, and avoiding swivel seats. With autonomous vehicles inching closer to reality, some companies may take these suggestions into serious consideration.

Elon Musk announced last month Tesla will introduce hands-free driving on Model S electric vehicles this summer via software update. Mercedes unveiled its vision for a "fully autonomous rolling lounge" at the Consumer Electronics Show earlier this year. And Delphi's autonomous Audi just completed a 3,400-mile trip across the country -- the longest autonomous vehicle journey to date.

“Is the real, fully driverless car -- where you push a button and the car pulls up to your house or place of work, picks you up then takes you to your destination without you having to do anything -- is that here? Is the Jetsons' car here? No," said Avery Ash, director of federal affairs for AAA, which tracks autonomous vehicle technology and its implications closely. "But so-called limited self-driving automation is very much here, and will continue to be rolled out across manufacturers over the next couple of years.”

Automating portions of a commute is expected to significantly reduce the likelihood of road accidents, 80 percent of which are caused by driver error. Because self-driving cars are aware of their surroundings, they can move fluidly in tandem with other vehicles, reducing congestion and saving time.

While the exact numbers are still uncertain, there's no debate that autonomous vehicles will significantly improve fuel efficiency. Volvo's platoon technology, for instance, where vehicles link up in a convoy and automatically maintain a safe distance without driver input, has been shown to allow for a 15 percent boost in fuel economy. In theory, the fuel savings could end up being much higher.

Autonomous cars also represent a big business opportunity. According to Lux Research, self-driving vehicles will create an $87 billion opportunity in 2030, with software companies benefiting the most. Lux predicts, however, that completely driverless cars will remain elusive.

"The consideration of motion sickness in the Michigan study is just one example from the much broader universe of issues and challenges that will come with new technologies at all levels of automation," said Ash.

One of the biggest issues AAA has identified is the transition between autonomous driving mode and a human taking control. People tend to be disoriented when they first take back the wheel, which creates a significant safety risk. There's also the larger issue of trust. While some people can't wait for a hands-free commute, others are wary.

It's noteworthy that 23 percent of the American adults UMTRI surveyed said they would not ride in an autonomous vehicle at all. And among those who would use a self-driving car, 46 percent said they would still watch the road.

“While the technology may one day be able to produce a fully autonomous experience, it’s still a pretty significant mental hurdle for many motorists," said Ash.

So even as autonomous vehicles become better prepared to cope with whatever the world throws at them, it seems humans will have to do a lot more work to prepare for autonomous vehicles.