It’s not often that auto industry bigwigs say they’re worried about selling too many cars. But that’s what Bill Ford, chair of Ford Motor Co., did this week at a conference in Barcelona. Ford said that with 1.2 billion cars and trucks on the world’s roads and another 144 million expected over the next four years, the industry’s biggest long-term risk is congested highways and urban traffic jams. “If we do nothing, it will limit the number of vehicles we can sell,” he said. The solution? Use mobile communications technology to allow cars to coordinate with each other and with traffic planning systems. Ford envisions a day when computers will do most of the driving in traffic, squeezing cars onto busy roads without compromising safety. The trend is already under way. The Ford Focus, for instance, can be equipped with cameras that scan for street signs, while an infrared warning system helps avoid fender-benders.