TriMet, more formally known as the Tri-County Metropolitan Transportation District of Oregon, is a public agency that operates mass transit in a region that spans most of the Portland metropolitan area in the U.S. state of Oregon. Created in 1969 by the Oregon legislature, the district replaced five private bus companies that operated in the three counties; Multnomah, Washington, and Clackamas. TriMet started operating a light rail system named MAX in 1986, and opened new lines in 1998 (Westside), 2001 (Airport), 2004 (Interstate Ave.), and 2009 (Clackamas), as well as a commuter rail line in 2009. It also runs the Portland Vintage Trolley on light rail lines in Downtown Portland and operates the City of Portland owned Portland Streetcar. - Source: Wikipedia