For the other type of simulation, Drive.ai uses data from real-world trips that the self-driving cars have already ingested, in the physical world, using their sensors. “We just take that logged data, and convert it into a scenario,” he says. That lets the researchers test several versions of their algorithms to see how each performs. For example, sometimes in the real world a self-driving car system will disengage—the human has to take over. In simulation, they can play that scenario over, and then try tweaking the software with the goal of the autonomous system handling that situation without disengaging.