The
R4 is a line of
Rodalies de Catalunya's Barcelona commuter rail service, operated by
Renfe Operadora. It runs northwards from the northern limits of the
province of Tarragona to
Barcelona, passing through the inland
Alt Penedès region. The line then continues towards
central Catalonia, describing a U-shaped route through the Barcelona area. According to 2008 data, the line's average weekday ridership is 105,935, the highest on any line of the Barcelona commuter rail service after the .