This has the most disputed metro line in Budapest. This line even appear on the first Budapest (heavy) metro line plan maps - heavy metro because there were many plans in Austria-Hungary related to the small underground [today M1], which were very different from the socialist metro plans). The first plans to begin the constructions of M4 were started in the early 1970s. In these plans this metro line would have run between Rákospalota residential district (lakótelep) and the industrial zone Budafok. The start of construction was planned for 1978, but it was cancelled. There were many plans and ideas after this. There were plans for French rubber-tyre metro or even with Ganz-Hunslet G5 type trains, a prototype Hungarian made train which had run between 1995-2000 on line 3.

Gábor Demszky, mayor of Budapest between 1990-2010, opted for a French-style metro, because he didn't want to build a Russian-style metro. All his election campaigns were based on the construction of the 4th metro line. The implementation plans had been completed by 1996, and the metro line was to be build with 70% EIB debt. This plan contained a station at Kosztolányi Dezsö tér instead of Bocskai út, because there was a Volánbusz coach station at that time. Later this bus station moved to Kelenföldi pályaudvar.

In 1997, tram lines 44 and 67 were abandoned due to the M4 plans. There were plans to abandon also tram lines 41, 47 and 49, but after the opening of the metro line. In 1998, the governemt of Fidesz party cancelled the metro project, because they considered it a luxury project. In 2002 and in 2006, MSZP won the elections, and they continued the plans. After all, this metro line could be constructed from EU funds.

In 2003 and 2004, two underpasses were built due to metro4 plans, at Móricz Zsigmond körtér and Bocskai út. In 2005 there was a new entrance built for the metro line 2 station at Keleti pályaudvar. The TBMs for M4 were eventually launched in 2006. There were many problems during the constructions, e.g. the TMB had to stop at Gellért tér, because Fövám tér wasn't ready to take the cutterheads.

There were plans to continue the line to Bosnyák tér, but when Fidesz won the elections in 2010, the leaders of Budapest decided not to continue with this extension. Nowadays, the mayor of Budapest István Tarlós is talking about an extension at the other end of the line, to Gazdagrét. This is not a new idea, it was also part of the 1996 plans, but the former government always wanted to build towards Bosnyák tér first.

Some trivia:
- There is a connecting tunnel between lines 2 and 3, but line 4 isn't connected to any other metro line.
- At Keleti pályaudvar, the station of line 4 isn't connected to line 2 via an underground passage, but just via the (partly open) mezzanine level.
- At Kálvin tér, there is a transfer tunnel for passengers below the line 3 station, although line 4 is above the M3 station.
- At Fövám tér, tram line 2 stops underground within the mezzanine of the metro station, but there was also a subsurface stop there before > photos.

(Thanks to Adam Kovacs)

Opened 28 March 2014

Keleti pályaudvar

M2

Tram

II. János Pál pápa tér

(planned as Népszínház utca)

Tram

Rákóczi tér

Tram

Kálvin tér

M3

Tram

Fövám tér

Tram

Szent Gellért tér – Müegyetem

Tram

Móricz Zsigmond körtér

Tram

Újbuda központ

(planned as Bocskai út)

Tram

Bikás park

(planned as Tétényi út)

Kelenföld vasútállomás

Tram

Photos © R. Schwandl