Google used to keep most details about its self-driving car program under wraps. But in the last few months, the self-driving car team—now a separate subsidiary called Waymo—has been making a concerted effort to open up and share key details with high-profile media outlets.

In May, Waymo revealed key details of its latest self-driving car design to Bloomberg as part of the rollout of a new program that ferries ordinary passengers around in Phoenix. Now The Atlantic's Alexis Madrigal has a new piece revealing important details about Waymo's extensive infrastructure for testing self-driving cars.

Madrigal reports on two Waymo projects that haven't been previously made public. One is an extensive virtual city in California, 100 miles east of Silicon Valley. Named Castle after the former Castle Air Force Base, the facility hosts a network of private roads for testing self-driving vehicles. It's a proprietary cousin of Mcity, the open vehicle testing facility we visited in 2015. At the Castle facility, Waymo builds replicas of real intersections—like a two-lane roundabout in Texas—that have given Waymo cars trouble.

"It's uncanny to pass from boulevards to neighborhood-ish streets with cement driveways to suburban intersections, minus the buildings we associate with these places," Madrigal writes.

Having their own extensive network of private streets allows Waymo engineers to perform repetitive tests to observe how Waymo's software reacts in carefully controlled situations. In one series of tests seen by Madrigal, another car cuts off a Waymo car at a variety of speeds and angles. The tests were designed to help engineers calibrate how hard cars brake in these kinds of situations. Brake too slowly and there's a risk of a crash. Brake too hard and passengers will get whiplash.

The Castle team has amassed an extensive collection of props—traffic cones, tricycles, fake plants, dummies—that help simulate a wide variety of road situations.

Waymo also gave Madrigal a look at Carcraft, the company's internal tool for building virtual worlds for Waymo cars to drive around in simulation. "At any time, there are now 25,000 virtual self-driving cars making their way through fully modeled versions of Austin, Mountain View, and Phoenix," Madrigal writes.

If a Google engineer notices an intersection that's giving Google's software trouble, she can pull that intersection up in Carcraft and observe the car's behavior in different scenarios—adding and moving cars, pedestrians, bicycles, and other obstacles. The software also makes it easy to run the same scenario thousands of times with varying initial conditions and detect cases where the car seems to be having difficulty.

"Waymo might simulate driving down a particularly tricky road hundreds of thousands of times in a single day," according to Madrigal. In 2016, the company logged nearly a thousand miles of simulated driving for every mile logged on real streets.

It's safe to assume that nothing about Madrigal's tour was random—that every step of the tour was carefully choreographed to tell the story Waymo wants to tell. And that story seems to be this: that Waymo's technology basically works and that they're now sweating all the little details that will transform a research prototype into a commercial product.

The first challenge when building a self-driving car is to make sure it follows the law and doesn't get in accidents. Waymo has made big strides on that front. Between 2015 and 2016, the average distance between disengagements—situations when a human driver had to take over from software control—increased roughly four-fold, from about 1,250 miles (2,000km) to 5,000 miles (8,000km). If that rate of progress continues, Waymo cars will be safer than human drivers in a few more years.

Safe AND smooth

But a great self-driving car product needs to do more than avoid crashes and follow traffic laws. It needs to provide a smooth, human-like ride, without abrupt stops, awkward pauses, or swerving. Most of the tests Madrigal observed were of this kind: the car could already drive in a safe and legal fashion, but the company was trying to make the ride smoother and more comfortable.

The May Bloomberg story also emphasized that the Phoenix trial is partly focused on the user interface. "In a mockup viewed by Bloomberg, a special dashboard displayed nearby cars, pedestrians, and buildings—an effort to give people confidence that the car is competent and in control," wrote Bloomberg's Mark Bergen and Alistair Barr.

This is not the behavior of a company that believes mass-market self-driving technology is still many years away. The broader goal of these carefully selected releases to Bloomberg, The Atlantic, and other publications is to convince the public that the company is crossing every "t" and dotting every "i." Waymo wants us to think that the technology will be safe, reliable, and maybe even boring when it's ultimately released to the public.

Of course, the fact that Waymo believes its technology is nearly ready for primetime doesn't make it so. It's possible the software has serious problems that aren't being surfaced by the company's extensive testing regime.

Disclosure: My brother works at Google.