Its aim is to connect three of the Budapest Helyiérdekű Vasút (BHÉV) suburban train lines, from Szentendre, Ráckeve and Csepel.

Population growth was especially strong in Buda and in Csepel island region, but the HÉV lines end at the boundaries of the downtown area, where passengers have to change to go into the city.

The council proposed to implement the investment between 2007 and 2010 with European Union funding, but this was rejected.

In 2007 deputy mayor Miklós Hagyó stated the council wanted to begin construction of the railway, and in February 2008, the Urban and Suburban Transport Association (VEKE) designed a four-track version of the metro line, now proposing to build the railway line from European Union sources between 2014 and 2020.

[1] On 14 April 2021 test excavations began as part of preparations for the first section between Közvágóhíd and Kálvin tér.