Skip to content
InfraWorldWide
← All projects
Railways

Sofia Metro Line M4 (Obelya – Sofia Airport)

The yellow line, 23.0 km with 20 stations, from the Obelya estate across the city to Terminal 2 of Vasil Levski Sofia Airport. For most of its length it has no tunnels of its own: between Slivnitsa and Mladost 1 it uses the line M1 tunnels built between 1998 and 2009. It is a branch in its own right only at the ends, in the 1.8 km Obelya spur opened in April 2003 and the eastern extensions to Tsarigradsko shose (2012) and the airport (2 April 2015). Trains through-run at Obelya onto line M2; until 26 August 2020 the airport service was signed as part of M2, and it was renumbered M4 in preparation for the infill station Pancho Vladigerov, which will physically separate the two lines and let them keep independent timetables. Since 19 July 2025 M4 has terminated at Slivnitsa while that station is built.

Total length
24 km
Open today
24 km
Sections
4

Includes 14 km whose works another project already measures, either as shared track or as a structure inside one of its sections. Counted in full here, and once in any total that spans projects.

Loading map data…

Sections

Sections of Sofia Metro Line M4 (Obelya – Sofia Airport): status, length, dates, cost, funding and contractors
SectionsStatusLengthTimelineCostFundingContractorsContract terms
Obelya spur: Obelya – Slivnitsa

1.8 km branch from Slivnitsa to the Obelya housing estate and depot, built as an extension of line 1 and opened on 20 April 2003. The infill station Pancho Vladigerov is under construction on this section; M4 has terminated at Slivnitsa since 19 July 2025

1
Opened2 km
  1. Apr 20, 2003Opened
––––
Slivnitsa – Mladost 1 (shared with M1)
Shared track Shared with Sofia Metro Line M1 (Slivnitsa – Business Park Sofia)

M4 trains use the line M1 tunnels between Slivnitsa and Mladost 1, opened in four steps between 28 January 1998 and 7 September 2009. Works began in 1979 at Vardar, on the first stage; the rest of the section was built in stages up to 2009. No length is published for the shared section on its own; 14.2 km is measured from the OpenStreetMap centreline and is consistent with the published 23.0 km line total

11011
Opened14 km
  1. 1979Construction start
  2. Sep 7, 2009Opened
–
  • National budgetSlivnitsa – Serdika (the first seven stations) and the tenth to thirteenth stations, up to Mladost 1, were built by the City of Sofia with its own funds (JBIC: "self-secured funds", "self-procured funds"). No amount published
  • LoanJBIC ODA loan BG-P5 to the City of Sofia, signed February 2002 (¥12,894 million), for the shield tunnel and stations from the seventh to the ninth station, Serdika – Vasil Levski Stadium
  • Taisei Corporation (shield tunnel, Serdika – Vasil Levski Stadium)Builder
–
Stage II, Lot 2: Mladost 1 – Tsarigradsko shose

Lot 2 of the second construction stage: 2.5 km and two underground stations, Mladost 3 and Inter Expo Center – Tsarigradsko shose. Works began 15 February 2009 and the section opened 25 April 2012. The 39-month contract for the section and the park-and-ride garage at Tsarigradsko shose was let at a tender price of €94 million (Investor.bg, June 2009). Built by the Metro Mladost consortium: PSI and Trace Sofia (both Trace Group Hold), Adval and Stroyinzhekt.

256
Opened3 km
  1. Feb 15, 2009Construction start
  2. Apr 25, 2012Opened
–
  • European UnionCohesion Fund grant of €200 million for the second construction stage, shared with the M2 section from Obelya to the Nadezhda overpass
  • Loan20% local co-financing by Sofia Municipality from a European Investment Bank loan
  • Обединение „Метро Младост”Builder
39 mo execution · Contract value €94M
Stage III, Lot 1: Tsarigradsko shose – Sofia Airport

Lot 1 of the third construction stage: 5 km and four stations (Druzhba, Iskarsko shose, Sofiyska Sveta Gora, Sofia Airport), two underground and two on the surface, reaching the Terminal 2 departures gate. Started 2013 and opened 2 April 2015; the three construction contracts, in force from 1 November 2012, totalled 136.05 million leva excluding VAT (23.5 + 63.6 + 48.95 million). At completion the investment was put at €75 million (Vestnik Stroitel, March 2015).

4789
Opened5 km
  1. 2013Construction start
  2. Apr 2, 2015Opened
  • Estimated €130MIndicative value under OP Transport, before bids were opened in February 2012.
  • Actual €75MInvestment at completion: about €16.5M (position I), €32.2M (II) and €25.46M (III).
  • European UnionOP Transport 2007–2013, Priority Axis 3: ERDF grant of €93 million towards the €110 million third construction stage, which also covered the M1 extension to Business Park Sofia
  • National budget
  • Обединение „Станилов – Метропроект” (position I, Tsarigradsko shose – Druzhba)Builder
  • Обединение „Метро Дружба” (position II, Druzhba – ul. Nedelcho Bonchev)Builder
  • Обединение „Метро Сифер” (position III, ul. Nedelcho Bonchev – Sofia Airport)Builder
Contract value лв136M

This section runs on track another line already owns. It counts in this line's length and is left out of every total that spans projects, so the kilometres are counted once.

Contractor roles are as recorded in the award. Only builders count toward the delivery rankings.

Funding

  • National budget19 km
    2 sections
    • Slivnitsa – Serdika (the first seven stations) and the tenth to thirteenth stations, up to Mladost 1, were built by the City of Sofia with its own funds (JBIC: "self-secured funds", "self-procured funds"). No amount published
  • Loan17 km
    2 sections
    • JBIC ODA loan BG-P5 to the City of Sofia, signed February 2002 (¥12,894 million), for the shield tunnel and stations from the seventh to the ninth station, Serdika – Vasil Levski Stadium
    • 20% local co-financing by Sofia Municipality from a European Investment Bank loan
  • European Union8 km
    2 sections
    • Cohesion Fund grant of €200 million for the second construction stage, shared with the M2 section from Obelya to the Nadezhda overpass
    • OP Transport 2007–2013, Priority Axis 3: ERDF grant of €93 million towards the €110 million third construction stage, which also covered the M1 extension to Business Park Sofia

A section that lists two sources counts its full length under each: the data records which sources paid, not what share each one carried.

Related projects

Sources

  1. Wikipedia: Sofia Metro
  2. Metropoliten Sofia: Second stage of the metro extension (OP Transport)
  3. Metropoliten Sofia: Third stage of the metro extension (OP Transport)
  4. Novinite: Subway Trains to Sofia Airport Start Running at 1 pm on April 2
  5. Investor.bg: Construction of the Tsarigradsko shose metro station begins (30 June 2009)read Sep 25, 2026
  6. Trace Group Hold: Sofia metro extension, Mladost 1 – Tsarigradsko shose sectionread Sep 25, 2026
  7. Gradat.bg: The metro through Druzhba, in a tunnel under the slope and on a viaduct to the airport (30 January 2012)read Sep 25, 2026
  8. Vestnik Stroitel: The metro extension to the airport is completing successfully (26 March 2015)read Sep 25, 2026
  9. Mediapool: The metro reaches Sofia Airport in 2015 (21 November 2012)read Sep 25, 2026
  10. Metropoliten: 20 години метро в София (2018-01)read Sep 28, 2026
  11. JBIC: ODA Loan Project Mid-Term Review 2006, Sofia Metro Extension Project (BG-P5) (2007)read Sep 28, 2026
  12. OpenStreetMap contributors (geometry, ODbL)