The Tren Urbano is a heavy-rail commuter metro system serving the cities of Bayamón, Guaynabo and San Juan. It is the only active rail system serving the general public in Puerto Rico, with 16 stations along a 10.7 mile (17.2 km). It is electrified by third rail at 750 V, d.c.. The line's construction started in July 1996 with the purpose of relieving traffic congestion in the San Juan metropolitan area, and was inaugurated January 2005 to mixed reactions. With a final estimated cost of $2.25 billion, nearly $1 billion more than original estimates,[11] the project has been criticized by government watchdogs, especially for its low passenger use of approximately 24,000 passengers daily (2005 est.), compared with original projections of 80,000 daily.[11]
There are current plans to extend the Tren Urbano rail system to outlying suburbs of the San Juan metro area, including a light interurban rail system from San Juan to Caguas scheduled to be completed in 2010.

wikipedia