Uber on Wednesday rolled out a fleet of self-driving cars in San Francisco, the second U.S. city to participate in its pilot project. Pittsburgh was the first. Riders who request an UberX — the lowest-priced Uber vehicle — will be matched with one of the self-driving Volvo XC90 SUVs if one is available and if the customers are willing, according to Anthony Levandowski, head of Uber’s Advanced Technology Group. They can accommodate three passengers. San Francisco “comes with its own nuances, including more bikes on the road, high traffic density and narrow lanes,” he noted.