It's all about balance when it comes to riding in self-driving cars.

The sensor-loaded cars pick up so much more information than a human driver can, what with their cameras, radar, LiDAR, and other sensing equipment. But that doesn't mean passengers want to know about each and every cyclist changing lanes, pedestrian crossing the street, or construction zone cone blocking the road.

So the first companies to offer a self-driving car service — like Waymo, the Google autonomous car spin-off — have to think about every ping, notification, and alert that plays through their app and in-car screens. The allure of self-driving cars, of course, is that here's a vehicle that can operate on its own, creating a "third space" that isn't home or the office. It's a space for you to chill or even sleep, to be productive or socialize, or to watch or listen to books, TV shows, movies, and other media. You might even ~ahem~ engage in other activities.

But to have that "third space" you have to trust the car, which takes a delicate balance: the vehicle sharing information with the passenger but not overwhelming them with data points. After all, your Uber driver doesn't shout about every car that merges into their lane, nor would you want them to.

Waymo's taxi service in the Phoenix area is called Waymo One, and for the past seven months, it's been picking up and dropping off about 1,000 riders in modified Chrysler Pacifica minivans. Its early rider program started in 2017 with a select, smaller group. Waymo's head of UX design and research, Ryan Powell, who develops the design and interfaces of the screens (including a mobile app) in the self-driving vehicles, thinks a lot about how to convey trustworthiness and vehicle competence without being overbearing.

"Time in the car becomes your own and how you want to use it," he said in a recent phone call. "We don't want to intrude. So we're judicious in how we choose to interrupt you."

Once in the car, Waymo has a few ways to communicate with riders: visually with onscreen messaging and images, and through sounds and noises. Although Waymo One still has safety operators in the front seat monitoring the Level 4 autonomous vehicle, eventually the service is supposed to be truly driverless.

Complex information is shared with a voice, like when you've arrived at your destination.

Other sounds or pings are meant to draw your attention to the screen. Waymo's pings are all set in the key of E, which has been shown to be calming, Powell said. (Google's chimes are in the key of G because, well, Google.) There's also a welcome chime and ambient sounds the car plays, since it's awkward to get into a completely quiet, empty car.

But Waymo is conscientious of its chimes and pings — if the car is slowing down for a cyclist, you won't be pinged. Instead, a message on the screen will say, "Yielding to cyclist." Again, it's that balance. The information-hungry rider can find out why the car is behaving a certain way, but the let-me-be rider can carry on without worrying about what the car is doing and why.

Touchscreens in the back of the car share information about your autonomous ride. Image: waymo

The two in-car screens on the back of the front seats are a crucial information tool. Instead of showing everything the car is picking up through its sensors, Waymo designers streamlined the 3D road view. Cars become simple shapes, pedestrians and cyclists have white and blue shadows under them, and buildings and scenery are dimmed. Laser points recreate the shape of pedestrians and bicyclists, emphasizing their importance. (Cars were originally replicated, but it was too much; now they're represented as blue rectangles.)

Riders just have to look up if they want to see more about what the car is up to — a progress bar and ETA stay up on the screen, as does a highlighted map route, traffic signals, school zones. "It's a more direct conversation with our riders," Powell said.

A Waymo rider can decide how much information they want to see while riding and can select a simple route view or a more detailed car view. "You’re deciding what level of information you want to receive," Powell said.

And just like that you're hearing, "We've arrived." Ride over.