Data gathered from Google’s self-driving Prius and Lexus cars shows that they are safer and smoother when steering themselves than when a human takes the wheel, according to the leader of Google’s autonomous-car project. Chris Urmson made those claims today at a robotics conference in Santa Clara, California. He presented results from two studies of data from the hundreds of thousands of miles Google’s vehicles have logged on public roads in California and Nevada. One of those analyses showed that when a human was behind the wheel, Google’s cars accelerated and braked significantly more sharply than they did when piloting themselves. Another showed that the cars’ software was much better at maintaining a safe distance from the vehicle ahead than the human drivers were. “We’re spending less time in near-collision states,” said Urmson.