Google says it has driven more than 2 million miles on public roads to test its vehicles
"In early 2015, we began to see some signs that we were getting close," Fairfield said. "The cars were going for longer and longer times without the humans having to intervene."
Fairfield said the company spent six months scrutinizing the vehicle's performance before Mahan was allowed to set out alone.
"That is a whole different beast, to get that driver out of the car, to take off the training wheels," Fairfield said.
Mahan said, "I had the greatest time driving around a neighborhood in Austin, Texas. It was so much fun, being aware that the vehicle was navigating intersections, and I was in good hands, perfectly safe."
The car Mahan rode in had a back up computers and multiple systems go control it.
"If you removed the driver from the loop you really have to have your backups," said Dmitri Dolgov, who heads Google's self-driving effort.
"There are millions of people like me, both blind or having other disabilities, or the situation of age, that would prevent me from driving," Mahan said. "This is a hope of independence. These cars will change the life prospects of people such as myself. I want very much to become a member of the driving public again."
Google also announced Tuesday that it was spinning off its self-driving car project into a company called Waymo, an independent division under Google's parent company, Alphabet.
Google was among the first technology companies to plunge into a province traditionally dominated by automakers in Detroit and elsewhere in the world. After initial testing by its employees, the company embraced a decision to put fully-autonomous cars on the road - likely without steering wheels or floor pedals - from the outset. In that decision, Google became an outlier, as the existing industry, mindful of their need to sell cars each year, took an approach intended to introduce self-driving features incrementally.
The Google announcement came on a day when federal regulators said they would move ahead with the formal rule-make process to allow computers on board cars to communicate directly with one another.
U.S. Transportation Secretary Anthony Foxx said a communication system among vehicles will "provide 360-degree situational awareness on the road and will help us enhance vehicle safety."
Vehicle to vehicle communication is considered an essential building block toward autonomous vehicles by some - but not all - of the companies working to develop them.
"If they're connected to each other, then we likely will not need signs, markings or even traffic signals," said Jim Barbaresso, vice president for intelligent transportation systems at HNTB Infrastructure Solutions.
"The infrastructure could change very dramatically. Cars could go through intersections without hitting each other, without the need of a traffic signal. We won't need wider lane widths any more, we can squeeze more lanes out of our existing highway footprints."
Fairfield said direct vehicle-to-vehicle communication was an asset, but less than essential, to putting autonomous cars on the road.
"It is useful, no question," Fairfield said. "There is vehicle technology where the car is telling you it's going to hit the brakes, or how much it's braking. That's somewhat useful, but we can [determine] that with radars and lasers and cameras, so it's not that useful."
Where communication among vehicles would be more useful, he said, was informing a vehicle computer of traffic jams or construction zones farther down the route in which the car is programmed to travel.
"You might want to route around it," Fairfield said. "It's not necessary, but it's useful. It's sort of like live updates to the max, so that all of our cars can intelligently avoid this."
