Auto sales plummeted again in January, falling to their lowest level in decades, as showroom traffic dropped by almost half and loans dried up even for interested consumers. The slowdown leaves the U.S. car industry at another historic crossroads. America has long served as the world's largest market for new cars. But Mike DiGiovanni, General Motors' director of global analysis, says more new vehicles were sold in China last month than in the U.S. The Chinese bought 760,000 vehicles, pushing that country's annual sales to 10.7 million units — greater than the current U.S. annual volume of 10 million. By contrast, in 2007, some 16 million vehicles were sold in North America.