The learning is constant. On the way back from the Highway 101 drive, for instance, an extra-long articulated bus turned in front of the Lexus, which was now back in human-driving mode because the software had been optimized for only highway driving that day. But all the sensors were still doing their jobs, so the bus showed up on Mr. Levandowski’s laptop screen as a string of red dots that stretched out as the bus rounded the corner