Welcome to Simulation City, the virtual world where Waymo tests its autonomous vehicles

A light gray cube with a thin blue top glides down a darkened highway, beset on all sides by dozens of green cubes. The green cubes bounce between lanes in an attempt to pass the gray cube, but the gray cube maintains a steady speed as the blackened landscape slips past into the artificial night. This is Simulation City, the virtual world where Waymo, an offshoot of Google, tests its autonomous vehicles in preparation for real-world experiences. The gray cube with the blue top represents one of the company's autonomous semi-trailer trucks, while the green cubes are all the other vehicles on the artificial highway. Waymo is unique among autonomous vehicle operators in that it has not one but two simulation programs it uses to train its vehicles.