The earliest attempts to implement an electrified suburban rail system in Warsaw were made in 1936–37, when the
Warsaw Railway Junction and surrounding railway lines were electrified to the national standard of 3 kV DC and high platform
electric multiple units were introduced (which later came to be designated
PKP class EW51). After World War II, newer EW53, EW54 and EW55 high-platform EMUs were introduced. In 1963,
Warszawa Śródmieście railway station was rebuilt into its current form as an underground city station in the city center and in 1967 the
Warsaw Cross-City Line was doubled to four tracks to enable separation of suburban and long-distance trains in preparation for the opening of
Warszawa Centralna railway station in 1975. The system went into steep decline from the late-1970s due to the country's serious economic problems and the
martial law period. These problems persisted well into the 1990s and 2000s as the fall of communism and the country's transition to a market economy made owning private cars more affordable to the general population and as a side effect of decentralization local authorities preferred to invest in infrastructure used directly by their constituencies. The Warsaw SKM in its current form was proposed in late-2002, stipulating to use the existing infrastructure of the Warsaw Railway Junction, especially the
cross city line with its over 2 km long tunnel running under the
city center and conveniently located underground station, as a cheap substitute for a
badly needed second metro line whose construction did not start until 2010. In order to implement this the then-
Mayor of Warsaw Lech Kaczyński established in 2004 the municipally owned company Szybka Kolej Miejska Sp. z o.o. The company was originally incorporated as a joint venture between the City of Warsaw with 50% shares and the companies Metro Warszawskie Sp. z o.o. with 49% shares and Tramwaje Warszawskie Sp. z. o.o. with 1% shares, both owned entirely by the city and responsible respectively for the Metro and Tram system. As such the company is notably completely independent from the national rail operator
PKP Group, unlike
Koleje Mazowieckie established by the
Masovian Voivodeship at around the same time. The newly formed company was equipped with six
Newag 14WE EMUs which were an extensive modernization of the
PKP class EN57 EMUs commonly used on regional routes at the time, with a modern looking body but retaining their original underframes. A year and a half after being established the SKM initiated its operation with its first trains, opening a single line from
Warszawa Zachodnia along the cross city line to
Warszawa Wschodnia and along the Vistula river to
Warszawa Falenica. The new service failed to deliver on its promise to serve as a viable replacement due to the poor state of the rail infrastructure. Passengers within the city center preferred the more accessible trams system and few people wanted to use the trains in the southeastern districts of the city. Additionally, while the integrated fare system of the Warsaw Transit Authority offered a large convenience the modern look and relative cleanness of the rolling stock sharply contrasted with the standard found in the Polish railroad; during rush hours most of the slots on the tracks were taken up by regional traffic and the new EMUs suffered from the same technical problems as the ones they were based on. Due to the initial low popularity of the line the original concept was somewhat altered in 2006 with the line extended outside the administrative borders of the city through the
Ursus district into the town of
Pruszków to the west and diverted to the district of the
Wesoła and the town of
Sulejówek to the east, turning the service into a suburban commuter network which allowed people in the
metropolitan area to quickly reach the city center and conveniently transfer within the city's public transit system. The revised formula proved to be very successful leading the city to take the purchase of all the shares of the company and purchase two more Newag 14WE EMUs. The popularity of the trains was also instrumental in the city negotiating a deal with the Masovian Voivodeship to have Koleje Mazowieckie honor long term tickets of the Warsaw Transit Authority, first along the route of the SKM and eventually within the entire area served by the city's public transit system. In 2010 the company purchased four brand new
Newag 19WE EMUs and opened a new line to the town of
Otwock. Additionally, the Warsaw Transit Authority signed a contract with the Koleje Mazowieckie to operate a line between
Warszawa Gdańska station on the Warsaw Circumferential Line and the town of
Legionowo under the branding of the SKM, and since 2012 taken over by the company. In 2011 13 new
Pesa Elf 27WE EMUs (2011–2012) were purchased. In 2012 a new
airport rail link was created running through the
Służewiec office district and a newly opened 1.5 km rail tunnel to
Warsaw Chopin Airport. In 2012 the company purchased 9 six car
Newag Impuls 35WE units. In 2020 SKM has awarded Newag a contract to supply an additional 21 Impuls 2 EMUs, 6 four car versions and 15 with five cars each. The trains feature air-conditioning, a passenger information system, ticket vending machines and validators,
Wi-Fi, USB sockets and an
AED defibrillator. In January 2022 Newag has delivered the first two Impuls 2 EMUs In June 2023, the S4 line was extended to
Zegrze Południowe, with two new stations: Wieliszew Centrum and Zegrze Południowe. (note: the Wieliszew Centrum station was not yet completed as of the extension's opening, but was completed later on) ==Rolling stock==