Line 13 of the Beijing Subway is a metro line that serves the northern suburbs of Beijing. On a map, Line 13's route is shaped like an inverted U that arcs north of the city and connects residential suburbs in Haidian, Changping, and Chaoyang Districts with the 2nd Ring Road and Line 2 at Xizhimen and Dongzhimen. With the exception of Dongzhimen and a tunnel between Xi'erqi and Longze, all of Line 13's tracks and stations are located on the surface or elevated above ground. The line is 40.85 km (25.38 mi) in length and 16 of its 17 stations are on the surface. Line 13's color is yellow on official maps, signage, and station branding. During rush hour, the section between Xizhimen and Wudaokou stations was reported in 2013 to be the second most congested section in the Beijing subway network, operating at 130% capacity.