Passengers are seen at the Songjiazhuang Transfer Station linking different subway lines in Beijing, capital of China, Dec. 30, 2012. Beijing put four subway lines into operation on Sunday, part of the city's efforts to expand rail transit to ease severe traffic congestion. The new lines bring the number of subway lines in Beijing to 16, with a total length of 442 kilometers, according to authorities. (Xinhua/Luo Xiaoguang)