The regional railway FR3 (until 2004 FM3) is a line of railway public transport part of the Lazio regional rail service. Connects Rome to Viterbo. In 2009, 2,130,777 were made train * km .
The FR3 uses the infrastructure of the railway line Rome-Capranica-Viterbo, about 88 km long  with double track from the departure station Roma Ostiense up to Cesano.
On this line are mainly used trains called TAF (Treno Alta Attendance). 
The numbering of the line (FR3) only appears in the information material (maps of public transport), in the official paper of Trenitalia and signs of some stations. In the scoreboards of the stations is only the initials R (regional train) and the number of the train.