In this photo Wednesday, May 14, 2014 file photo, a Google self-driving car is on exhibit at the Computer History Museum in Mountain View, Calif. The head of self-driving cars for Google on Wednesday, Jan. 14, 2015 said he expects real people to be using them on public roads in two to five years. (AP Photo/Eric Risberg, File)

The head of self-driving cars for Google expects real people to be using them on public roads in two to five years.

Chris Urmson says the cars would still be test vehicles, and Google would collect data on how they interact with other vehicles and pedestrians.

Google is working on sensors to detect road signs and other vehicles, and software that analyzes all the data. The small, bulbous cars without steering wheels or pedals are being tested at a Google facility in California.

Urmson wouldn't give a date for putting driverless cars on roads en masse, saying that the system has to be safe enough to work properly.

He told reporters Wednesday at the Automotive News World Congress in Detroit that Google doesn't know yet how it will make money on the cars.

Urmson 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 may face state regulatory hurdles depending on where it chooses to test the cars in public. Under legislation that Google persuaded California lawmakers 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 in December announced that it had a fully functioning prototype that's 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.

Google also confirmed that it has hired Roush Enterprises Inc., a Detroit-area company that designs and builds prototypes for the auto industry, to build 150 prototype Google autonomous cars.

Urmson said Google is making laser and other sensors for the cars smaller and less costly.

He predicted that the cars would fail at some point on public roads, but said Google's cars have been driven more than 700,000 miles on public roads without causing a crash.

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