“My read on Google’s approach is, how do you create vehicles that are smart enough to drive on existing roadways,” Mr. Mahan said in a phone interview. “They’re looking at a paradigm shift in transportation, where the vehicles assume all of the driving tasks for efficiency and safety.”

He added: “I’ve been in the Google cars quite a bit in urban traffic and highway. The technology is incredibly capable. They drive like good drivers. I spoke to a programmer who helps define how the car behaves. I told him, ‘So you’re the person who made these cars drive like my wife.’ ”

Google’s driverless vehicle is in testing. Because California law requires that self-driving vehicles be fitted with backup manual systems, the company has installed a temporary steering wheel and controls. On a website devoted to the car, Google said, “We’ll remove these manual controls after the prototypes have finished being tested and permitted, because our vehicles are ultimately designed to operate without a human driver.”

The marketplace — together with regulators — could have the final say as to what type of autonomous car is ultimately offered for sale and whether the vehicle could accommodate those incapable of controlling the car manually.

Research doesn’t suggest that a clear majority of drivers are eager to turn the wheel over to a robotic driver. A survey by the Pew Research Center and Smithsonian magazine, for example, found that 48 percent of Americans would be interested in a self-driving car; 50 percent would not. The survey did not attempt to determine whether those who were accepting of self-driving technology would be willing to relinquish all control to a vehicle without a steering wheel or brake pedal.

The National Highway Transportation Safety Administration has not issued regulations for self-driving vehicles, and it would not comment for the record in regard to potential rules. But it has issued guidelines for on-road testing and advised the states in regard to on-road operation.

In a statement, the safety agency said that fully automated vehicles required further testing and should be equipped with backup steering and brake controls during the testing period. That means that a driver must be capable of taking control of the vehicle — an action that may not be feasible for people with severe disabilities.