The online survey involving 618 respondents showed that 37.2% were "very concerned" about riding in a completely self-driving vehicle, while 66.6% were "very or moderately concerned."
Only 9.7% of respondents said they were not at all concerned about riding in a completely self-driving vehicle.
The most frequent preference was for no self-driving (45.8%), followed by partially self-driving (38.7%), with completely self-driving being preferred by only 15.5% of respondents.
Women expressed greater concern than men about riding in completely self-driving vehicles: 43% indicated they were "very concerned," versus 31.3% of men. The difference was smaller for partially self-driving vehicles, where only 17.5% of women were very concerned versus 16.4% of men.
The survey and report is part of a series of eight that address public opinion, human factors and safety-related issues concerning self-driving vehicles.
In a previous survey released last month, researchers Brandon Schoettle and Michael Sivak of the U-M Transportation Research Institute asked respondents about their familiarity with and general opinion about connected vehicles, as well as perceived benefits and concerns with using the technology.
The U-M poll found that about 30% of nearly 1,600 online respondents in the U.S., Australia and the U.K. are "very concerned" about system and vehicle security breaches from hackers and about data privacy in tracking speed and location. Another 37% are "moderately concerned" about these issues; and nearly a quarter are "slightly concerned."
In addition to security and privacy fears, a majority of those surveyed expressed concern about system failure and performance, especially in bad weather, and believe drivers will rely too much on the technology or be distracted by it.
Last year, in an identical survey involving 618 respondents, only a small percentage of drivers said they would be completely comfortable in a driverless car, while a sizable number indicated they would have no problem as long as they retain "some control."
The survey was developed to examine motorists' preferences among levels of vehicle automation, including preferences for interacting with and overall concern about riding in self-driving vehicles.
In addition to a fear over the loss of vehicle control, drivers cited concerns over motion sickness, which they expected to be more of an issue in self-driving vehicles than in conventional vehicles.
"The reason is that the three main factors contributing to motion sickness [conflict between vestibular and visual inputs, inability to anticipate the direction of motion, and lack of control over the direction of motion] are elevated in self-driving vehicles," the researchers stated in their report. "However, the frequency and severity of motion sickness is influenced by the activity that one would be involved in instead of driving."
The survey's results indicate that, for example, 6% to 10% of American adults riding in fully self-driving vehicles would be expected to "often, usually, or always experience some level of motion sickness."
Analogously, 6% to 12% of American adults riding in fully self-driving vehicles would be likely to experience moderate or severe motion sickness at some point.