The regional railway FR4 is the name of a line of railway public transport part of the Lazio regional rail service. In 2009, 1,210,272 were made train.
The line FR4 uses the infrastructure of the railway lines Rome-Albano, Rome-Frascati and Rome-Velletri which are developed respectively for 28 km, 23 km and 41 km.
The rolling stock used is heterogeneous.
The trains travel in common with the line FR6 the stretch between Roma Termini and Ciampino from this locality are directed respectively to Frascati, Albano and Velletri Lazio.
The numbering of the line (FR4) only appears in the information material (maps of public transport) and in the signs of some stations. In the scoreboards of the stations is only the initials R and the numbering of the race.