Railway lines departed from Warsaw in a radial arrangement and were connected by a ring line. The capital city of a revived Poland needed an enhanced transport system. In 1918 the Ministry of Railways (still under German occupation) established the Committee for the Reconstruction of the Warsaw Railway Junction headed by Professor Aleksander Wasiutyński. As a result, in July 1919 the Seym adopted an act on the reconstruction of the Warsaw railway junction, signed along with the decree concerning the expropriation of land for the purposes of the aforementioned investment by the Head of State, Józef Piłsudski.
Goods traffic was to be routed on the old ring rail line, whereas passenger traffic, on the cross-city line passing through the centre of Warsaw, continuing on the bridge across the Vistula to Warszawa Wschodnia (Eastern Warsaw) station. A provisional main railway station, Warszawa Główna, was built along with holding stations Warszawa Szczęśliwice and Warszawa Grochów. In the centre tracks were laid in a cut and 0.6 mile (1 km) long tunnel under Aleje Jerozolimskie and further on the new bridge across the Vistula. But, a significant problem emerged: steam locomotives could not run in a long tunnel. This had a predominant effect on the commencement of electrification of the Warsaw junction.
In 1919, Professor Roman Podoski set up an inter-ministry Railway Electrification Studies Bureau. Based on analyses carried out in 1921, a system of 3 kV direct current generated by rectifier substations erected approximately every 16 miles (25 km) along the line. The government was made to electrify the whole Warsaw junction stage by stage and detailed designs were developed. Equipment and vehicles were supplied by UK manufacturers: English Electric and Metropolitan Vickers. The English set up the technical and commercial Contractors Committee for the Electrification of Polish Railways with an office in Warsaw. As agreed, everything that could be manufactured in Poland was produced on site.
A huge amount of work was performed over 3 years. 66 miles (106 km) of railway lines, 12 stations and 18 stops, 62 miles (100 km) of feeders, 6 traction substations, and 162 miles (260 km) of traction network were reconstructed and electrified. Also 2 electric locomotive depots and main electric traction workshops were built. 76 three-wagon electric units E91 and E92, fitted with equipment of English origin were built. They could carry 536 passengers. In addition, 6 four-axle EL.100 “heavyweight” locomotives (including 4 built in Chrzanów) and 4 four-axle EL.200 “lightweight” locomotives built in the Cegielski Factory were produced. On 15 December 1936 the first electrified section, Pruszków – Warsaw – Otwock, was put into service. Six months later, an electric train arrived in Grodzisk and Żyrardów, and in December 1937 – in Mińsk Mazowiecki.
Apart from electrifying the railway network before the outbreak of war, Polish State Railways introduced modern teletechnical equipment on a large scale. This involved the laying of teletechnical cable lines, the introduction of teleprinters, new automatic exchanges, telephone equipment, dispatching units and counter safety locks, aerial networks, etc.
From 1927 the privately-owned Electric Commuter Railway was in operation in Warsaw. It was supplied with 600 V DC and provided suburban passenger traffic services on the Warsaw – Komorów – Podkowa Leśna – Grodzisk Mazowiecki route, with annexed connections to Włochy and Milanówek.