Line 4 is a loop line of the Shanghai Metro network. Its rolling stock carry a bright violet colour belt to differentiate them from Line 3 trains which share a portion of its track. To determine the direction of travel, the line that travels counter-clockwise is called the Outer Loop (外环), while the other line is known as the Inner Loop (内环). Although it is a loop line, trains returning to the depot use Yishan Road as a terminal to let all passengers disembark. The first segment of the line between Damuqiao Road and Lancun Road (running in a "C"-shape) opened on December 31, 2005. The remainder of the line opened on December 29, 2007. The line is colored purple on system maps.