“Sex and the City” star Chris Noth is used to stopping traffic, but accidents are rare. Two paparazzi on bikes collided as they raced to take his picture in the East Village yesterday. “He was alone in dark sunglasses, looking very Mr. Big,” a spy told us. “Nobody bothered him until there was suddenly a huge fracas as two photographers screeched in on bikes and literally crashed into each other. But they were not hurt and immediately jumped up to take pictures of him. He played it cool.”