Warsaw–Grodzisk Mazowiecki railway

The Warsaw–Grodzisk Mazowiecki railway is a 30 kilometer long, double-tracked, electrified suburban railway line connecting Warszawa Zachodnia station in Warsaw with Grodzisk Mazowiecki railway station in Grodzisk Mazowiecki. The line is designated by the Polish national railway infrastructure manager PKP Polskie Linie Kolejowe as rail line number 447.

It runs along the long-distance Warsaw–Katowice line, extending the suburban tracks of the Warsaw Cross-City line westward. The line is dedicated for use by local traffic, however both lines are technically capable of carrying all types of trains, effectively forming a four track rail corridor running roughly East-West through the center of the Warsaw metropolitan area.

Opening
The line was originally opened in 1845 as part of Warsaw–Vienna railway and electrified between 1936 and 1937. During the interbellum with the construction of the Warsaw Cross-City line authorities planned to upgrade the line to four tracks, but delayed the investment due to lack of funding. A second set of tracks was built only in 1959, since then the original southern tracks, today designated as line number 447, are dedicated for suburban connections, while the newer northern ones running parallel to them, today a part of line number 1, serve long-distance passenger and goods trains.

Modernization
In November 2015 PKP PLK announced a tender for the modernization of the line on the section between Warszawa Włochy railway station and Grodzisk Mazowiecki. As part of modernization, which was to improve movements in the Warsaw agglomeration, the stations on the line were rebuilt and a new station in Parzniew was built. After completion of the work the line speed increased from 60–80 km/h to 120 km/h. Works were carried out between the years 2016–2019.

Usage
The line is used by Koleje Mazowieckie and Szybka Kolej Miejska (the latter one only between Warsaw and Pruszków).