The Tren Urbano, an elevated light-rail system, travels throughout the metropolitan area, with stops at the University of Puerto Rico and Bayamón, but does not stop near the main tourist areas or at the airport. The fare is $1.50, which includes transfers to city buses. The system runs from 5:30 AM to 11 PM. It's run by the Alternativa de Transporte Integrado, better known as the ATI.
Alternativa de Transporte Integrado (787/723-3760. www.ati.gobierno.pr).