High Quality Content by WIKIPEDIA articles! Metro Light Rail (styled corporately as METRO) is a 32 km (20 mi.) light rail line operating in the U.S. state of Arizona. Part of the Valley Metro public transit system, it serves the cities of Phoenix, Tempe, and Mesa. Construction began in March 2005; operation started December 27, 2008. The line has 2011 estimated daily ridership of 41,300, making it the 12th busiest light rail system in the country.