CO.TRA.L buses run frequently (every 15 minutes) from Ponte Mammolo metro station, line B (remember to buy your tickets in advance from the kiosk at Ponte Mammolo, and to validate them when you get on the bus). The bus stops to Tivoli Terme.
F.F.S.S. train Rome-Pescara line from Tiburtina station approxly every half hour. The train stops at Tivoli Terme (or Bagni di Tivoli) station.