The D Line – also referred to as the Green Line, because green is the line's color on maps – is a light rail line which is part of the light rail system operated by the Regional Transportation District in the Denver–Aurora Metropolitan Area in Colorado. The D line was the first line in the system when it opened in 1994, traveling from downtown Denver to I-25 and Broadway as the Central Corridor. It was extended along the Southwest Corridor in July 2000. Because it was the first and only line in the system it had no letter or color designation until the Central Platte Valley Spur opened on April 5, 2002, although on maps it was designated as Route 101.