That has put automakers in an awkward spot to reach car buyers who are drawn to the idea of driving with fewer dangers and drudgeries but are still leery of self-driving technology. To win them over, carmakers increasingly are selling the illusion of control while, in practice, taking more and more away.
"The technology is probably the easiest problem to solve," said Jeremy Carlson, a senior analyst for IHS Automotive. "Consumer acceptance might be the hardest."
Cars and trucks with driver-assisting technology, a recent Boston Consulting Group report predicts, will hit the roads in "large numbers" by 2017 and at increasingly affordable prices.
Packages that sold for $4,000 a few years ago now leave the lot at half the price. Lexus's new RX will offer upgrades that stop the SUV in case of a potential crash and sound an alarm if it veers out of lane for about $500.
Rather than one revelatory self-driving debut, analysts believe this steady march of what the industry calls "semi-driverless" upgrades will persuade people to finally give up the wheel.
Loaded with cameras, sensors and computing power, the cars have, in tests, performed sharper and more consistently than human drivers without fear of drowsiness, drunkenness or distraction.
Yet the tension comes from a puzzling inconsistency traced in a survey by AutoTrader.com, which found that although most Americans say they are unnerved by ceding total control to a driverless car, they're happy to pay for all the piecemeal upgrades on which that car is built.
"When polls ask about driverless cars, people are nervous, they're fearful," said Michelle Krebs, a senior analyst with AutoTrader. "But when you ask them about all these individual technologies - lane assist, helped parking - they say, yeah, we want all those."
Researchers at HERE, a Nokia offshoot building maps for self-driving cars, also found a similar impression in surveys. Drivers still believe that cars make their lives easier, more free, more fun - though they also crave the next big thing, even if it weirds them out.
Industry officials acknowledge that self-driving cars may never be universally accepted by drivers, especially those who value being in control of their car. In the self-driving mode of Mercedes' F 015 concept car, for instance, passengers can't steer or brake and can use a touchscreen to request the car to speed up or slow down - but only if the car thinks that's a good idea.
But engineers have made efforts to make the driverless tech act more familiar and human. In some earlier Volvos, for instance, the automatic brakes allowed such a wide and safe distance from the car ahead that the feature annoyed many drivers, who ended up disengaging it altogether.
The updated feature stops the car far closer, Volvo technology spokesman Jim Nichols said, in hopes "the driver doesn't have the desire to turn the feature off."
Where the cars once made their decisions silently, they have begun to sound out their thinking in ways that drivers can understand. Cars will now explain their sudden slowing by saying, for instance, "Crosswalk ahead," and dashboard screens will show directions and obstacles such as construction or broken-down vehicles.
But they are also designed not to be overly obtrusive. If too many unsignaled lane changes or other errors lead the safety system in Volvo's newer S60 sedans to believe its driver is losing attentiveness, the car's dashboard will flash a coffee cup and the words, "Time for a break."
For the XC90, Volvo's "semi-driverless" crossover SUV, sound engineers measured drivers' reaction times and led focus groups in several countries to gauge which of a series of specialized chimes showed the "appropriate urgency." The big question: Should warning sounds be calming and subtle, to not shock the passenger, or shrill and insistent, to underscore how important it is for the computer to take the wheel?
The answer, Volvo's Nichols said, was both. The car was given "psychoacoustic design elements" to heighten drivers' focus on their surroundings when necessary, while less-urgent sounds were designed to be "much more calming, almost a melody."
Automakers' worry concerning the mixed feelings about driverless technology has kept several big safety improvements off American roads.
In Europe, Ford sells cars with sign-reading "Intelligent Speed Limiters" that ensure drivers can't sail above the speed limit. Yet despite the safety benefits, Ford has not rolled the tech onto American roads because of concerns that drivers here may simply steer clear.
"There's not a technical impediment," said Alan Hall, a Ford spokesman. "The most important part is if they're willing to pay for it."
Ultimately, car companies and their engineers hope the benefits of driverless technology, which offers a relief from the annoyances of highway commutes and heavy traffic, will persuade buyers to let go of the wheel.
"Today, when you sit in a car, it doesn't feel like freedom. You feel frustrated. What you'd rather do, you can't do, because you're stuck in a traffic jam," said Erik Coelingh, a Volvo senior technical leader in Sweden. "I don't know if it's old-fashioned, but we still think it's a lot of fun to drive a car. For many customers that . . . is really important. We don't want to take that away."
