Google's driverless cars have already clocked an astonishing 2m miles on the roads, it has revealed, as the journey towards a driver free future ramps up.
The tech company has passed the milestone in just 16 months since it last passed the 1m mark on the roads of California – it originally took it six years to reach that first million.
It's racked up the equivalent of 300 years of driving experience, said Google's head of self-driving technology Dmitri Dolgov.
"What takes a self-driving car from concept, to demonstration, and finally to reality is this accumulated experience," he said in a blog post.
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"Even in the early days of our project, it didn’t take long before we could give a good demo ride in our self-driving car. That’s because it’s relatively easy to master the first 90 per cent of driving where you’re travelling on freeways, navigating light city-street traffic, or making your way through simple intersections."
Now, the firm is working on the "final 10 per cent" – mastering the more difficult tasks, routes and conditions required by the cars.
"Our cars have gotten much better at detecting and responding to everything from crossing guards to emergency vehicles to construction zones. With these advanced driving skills, we can adjust to things like sudden changes in road conditions, such as closed lanes," said Dolgov.
A major part of the development of driverless cars is understanding people, the executive explained. The car must be able to gauge how bikes, other cars and pedestrians will act and be able to interact with them rather than simply navigating around them.
"In a delicate social dance, people signal their intentions in a number of ways… Our cars can often mimic these social behaviours and communicate our intentions to other drivers, while reading many cues that tell us if we’re able to pass, cut in or merge," he said.
Google is far from the only company – tech or automotive – working on driverless car technology.
Uber last month put its first self-driving taxis on the road in Pittsburgh, even letting ordinary travellers order one (with an engineer ready to take the wheel at any time… just in case). However, it was pipped to the post of being the first when under the radar startup NuTonomy put its own self-driving taxis on the road earlier in the summer.