Metro Line M3 (Budapest Metro)

The Mayor of Budapest Gábor Demszky was warned in 2006[7] by BKV that the line would soon need reconstruction, but no steps towards this were made before the new mayor István Tarlós took office in 2010. Some trains were prone to burning or smoking issues, but this had caused neither fatalities nor serious injuries so far. Tarlós reacted by ordering the retirement of all trains that were more than 40 years old. He also started the reconstruction of the tracks, because they were reported as hazardous. In 2014, the mayor's administration published the plans for the complete reconstruction of the line and Viktor Orbán's government allowed the local government to finance the reconstruction of the trains by taking up loans. Repayment of the loans was guaranteed by the national government in case the municipal government was not able to pay. The municipal government requested EU funds to finance the reconstruction of the underground infrastructure (tunnels and stations), and the national government guaranteed that it would provide additional financing in case insufficient EU funds were obtained.

In January 2016 the first train for reconstruction was handed over to the Russian Metrowagonmash (the original manufacturer).[8] Tarlós had preferred buying new trains, but was overruled by the Orbán government.[9] The prototype of the reconstructed trains entered service on 20 March 2017.[10] From then on, the number of reconstructed trains serving the line was scheduled to increase by 2 trains every month, and from April 3, 2018 onward, only reconstructed trains run on this line.

On 4 September, 2017 contracts for reconstructing the tunnel and stations of the northern section (Dózsa György út – Újpest-Központ) were signed. The stations were to be finished by 31 December 2018, but in fact were only reopened on 30 March 2019. After the reopening of the stations, Újpest-Központ was renamed to Újpest-központ, to be in line with metro line M4's Újbuda-központ station and Újpest-Városkapu, originally planned to be renamed to Újpest vasútállomás to help navigation, ended up being renamed to Újpest-városkapu. Árpád híd station was planned to be renamed to Göncz Árpád városközpont, but only ended up being renamed in January 2020. Dózsa György út station had to be closed from 14 May 2022 all the way until 22 May 2023, as there wasn't an elevator installed when the station reopened, and was only reopened when the full reconstructed line was able to be used. The reconstruction of the southern section (Népliget – Kőbánya–Kispest) was started on 6 April 2019. On 22 October 2020, the southern, renovated section of line M3 was opened. Originally, Kőbánya-Kispest station was planned to be renamed to Kőbánya-Kispest vasútállomás, for a similar reason as Újpest-városkapu, but this change never took place. The reconstruction of the middle section (Klinikák – Lehel tér) started on March 7, 2020 with Arany János utca and Ferenciek tere stations,[11] Corvin-negyed and Klinikák stations on July 11, 2020 and Deák Ferenc tér, Nyugati pályaudvar and Kálvin tér stations on 7 November, 2020. The stations slowly reopened, with Klinikák (renamed to Semmelweis Klinikák), Corvin-negyed and Kálvin tér stations reopening on 16 May 2022, Ferenciek tere and Deák Ferenc stations on 23 January 2023, and with Arany János utca and Nyugati pályaudvar stations on 20 March 2023, the line operated in one section once again, instead of the previous 2 (Kőbánya-Kispest – Kálvin tér, Göncz Árpád városközpont – Újpest-központ) sections. Finally, on 22 May 2023, with Nagyvárad tér and Lehel tér stations, the 5-and-a-half-year long reconstruction finished. After this reconstruction, the renewed trains will probably stay in service for more than 20 years before having to be replaced.[12]

Civil groups voiced their concerns over the lack of accessibility and air-conditioning.[13] In response, Tarlós promised modular AC units would be installed on the trains and the government agreed to make all 20 stations accessible.[14][15][16]