The Rhymney line is a commuter rail line running from Cardiff Central through the Rhymney valley via Heath and Llanishen in the north of the city, to Caerphilly, Bargoed and Rhymney.

Urban and suburban rail plays a key role in public transport in many of the major cities of the United Kingdom. Urban rail refers to the train service between city centres and suburbs or nearby towns that acts as a main mode of transport for travellers on a daily basis. They consist of several railway lines connecting city centre stations of major cities to suburbs and surrounding towns.