Waymo on Wednesday launched a commercial robot ride-hailing service in Arizona called Waymo One. Like Uber or Lyft, customers will summon a ride with a smartphone app. But in this case, the car will be driving itself. Only “a few hundred customers” will have access to the app and participate in the early stages. Although the cars will drive themselves, a Waymo engineer will sit behind the wheel in case anything goes wrong. Waymo did not say when the cars will start arriving without a human minder or when the program will be expanded. Waymo’s cars, Chrysler Pacifica minivans bristling...