Chris Urmson said the cars would still be test vehicles and Google would collect data on how they interacted with other vehicles and pedestrians.
The tech company is working on sensors to detect road signs and other vehicles and software that analyses all the data. The small, bulbous cars without steering wheels or pedals are being tested at a Google centre in California.
Mr Urmson would not give a date for putting driver-less cars on roads en masse, saying the system had to be safe enough to work properly.
He told reporters at the Automotive News World Congress in Detroit, Michigan, that Google did not yet know how it would make money on the cars. Mr Urmson says he wants to reach the point where his test team no longer has to pilot the cars.
“What we really need is to get to the point where we’re learning about how people interact with it, how they are using it, and how can we best bring that to market as a product that people care for,” he said.
Google, based in Mountain View, California, may face state regulatory hurdles depending on where it chooses to test the cars in public.
Under legislation that Google persuaded California politicians to pass in 2012, self-driving cars must have a steering wheel and pedals. Several other states have passed laws formally allowing autonomous cars on public roads without that restriction.
The company announced in December it had a fully functioning prototype that had been driving on its test track. It hoped to see the cars on the road in northern California this year, but they would have to have safety drivers and temporary manual controls.