The young country had to face an important task. The arrangement and routing of railways matched the economic and military needs of each of the occupying forces. The entity formed after the integration of three railway networks lacked direct connections between important economic centres: Silesia and Kraków were not connected to Warsaw and the coast, Greater Poland had no railway connection with Warsaw and local connections were scarce on both sides of the old boundaries between the former partitioned territories.
One of the first newly built lines was the Kutno – Koło – Konin – Strzał-kowo line (1921), shortening the passage from Poznań to Warsaw, and the Gdynia – Kokoszki line (1921), bypas-sing the Free City of Danzig. Also, Puck was connected to Hel. Railway sidings were built in Upper Silesia, including: the Hajduki – Kochłowice siding (1924), bypassing the German junction in Gliwice, Mako-szowy-Mizerów siding (1924), Brzezie – Bluszczów siding (1925), connecting the Polish railway network with the western part of Upper Silesia, Pawłowice Śląskie – Chybie siding (1924), and Chorzów – Szarlej siding (1925) bypassing the Bytom junction. The military narrow-gauge line between Nasielsk and Sierpc was replaced with a normal-gauge line (1924).
Coal was transported from Silesia to the northern parts of Poland a long way through Częstochowa and Warsaw. Unfortunately, the stations on the former Warsaw-Vienna Railroad were not capable of ensuring efficient railway traffic. Thus, the stations in Częstochowa and Łazy were first expanded. Trains from Upper Silesia ran in transit to Greater Poland through the German territory on the Lubliniec – Olesno – Kluczbork line, which considerably increased the cost of transport. The customs war between Poland and Germany, which started in 1925, accelerated the decision to build the Kalety – Herby – Wieluń – Podzamcze line continuing via Kępno to Greater Poland. The 114-kilometre long single track line (although the route was prepared for a double track line) with 8 stations and a passing loop, designed by a team of young engineers under the supervision of Józef Nowkuński, was opened after little more than one year from construction commencing (1926). Its significance is testified by the fact that in 1928 as many as 32 pairs of freight trains (more than half of which weighed 2 thousand tons) were in operation on that line. A second track was laid one year later. In 1927, 5 thousand wagons a day departed from the expanded station in Tarnowskie Góry.
The lines: Płock – Kutno – Zgierz (1925), Nasielsk – Sierpc – Toruń (1937) and Płock – Sierpc – Brodnica (1937) filled the gaps in the railway network in the territory that was formerly under Russian rule. The Warsaw – Radom and Tunel – Kraków connection (1934) brought the city of Krakus closer to the capital city of Poland. Also, large freight stations in Katowice Ligota, Chybie, Czarnolesie, Wodzisław Śląski and Rybnik and the former border stations in Sosnowiec, Mysłowice, Szczakowa, Trzebinia, Dąbrowa Górnicza and Będzin were modernised.
The largest railway investment in the interwar period, completed in 1928 – 1933, was the 301 mile (485 kilometres) long Silesia-Ports coal trunk line. Built by the state and completed by joint stock company French-Polish Rail Association, the line started in Herby and ran through Chorzew Siemkowice – Zduńska Wola Karsznice (1930) – Inowrocław (1933) – Nowa Wieś Wielka – Bydgoszcz Wschód (1930) – Maksymilianowo (1928) – Wierzchucin (1930) – Bąk (1930) – Kościerzyna (1928) – Somonino to Gdynia (1930). The route covered existing sections, made available by the Polish State Railways in exchange for allowing their own passenger traffic on that line. The line was the backbone of railway transport in the Second Polish Republic.
In Gdynia, the construction of the seaport coincided with the building of a modern port station with many groups of tracks that were 169 miles (272 kilometres) long, with a shunting yard fitted with the then state-of-the-art coal transfer equipment such as cranes and wagon tipplers. It could unload 3,600 wagons in 60 trains a day.
Traction services were provided by 126 Ty23 type steam locomotives parked in the engine houses in Karsznice (62 vehicles) and Kapuściska (64 vehicles). The railway, popularly referred to as the “French rail”, alleviated other lines from the transport of coal which accounted for 98% of cargo transit on that route. Over 18 years the Polish State Railways built about 1,025 miles (1,650 km) of lines in total.
In 1927 a system enabling the transportation of perishable goods was put into operation. Such goods were transported in freezer cars on appointed routes, along which dry ice stores were maintained at major stations (also on the frontier). This facilitated the transit of, for example: meat from Romania to France, fish from Latvia to Poland, meat from Poland to Germany, France and Switzerland, and bacon, poultry, butter and eggs to England by means of 550 freight wagons (1939). Trains with wagons cooled by dry ice completed the longest route of 699 miles (1,225 km) from Zalischyki to the port in Gdynia in a few days. The only manufacturer of dry ice was located in Krynica, from where ice in special containers was supplied to various storage facilities. During the times of imperial and royal rule it took 54 hours for such trains to travel from Stanislaviv to Vienna, 43 hours from Lviv, and 18 hours from Kraków. The Polish State Railways transported up to 85.9 million tons of goods per year (1929).
In the interwar period trains were assigned a different priority. The highest priority had rescue trains on their way to an accident site, followed by: first degree of seniority (luxury, courier, fast trains), second degree (passenger limited stop, passenger, suburban, mixed passenger and freight, military and sanitary, service and inspection trains), third degree (mixed freight and passenger, fast freight trains, freight trains carrying food, and long-distance freight trains) and fourth degree (wagon transfer trains). Trains of international significance passing through Poland were, among other lines, Nord Express from Paris (Calais and Ostend) via Cologne, Hannover, Berlin (where it was split into 3 parts), Frankfurt on the Oder, Poznań, and Kutno to Warsaw. The second part from Berlin travelled through Frankfurt on the Oder, Krzyż, Piła, Chojnice, Tczew, Malbork, Königsberg (Kaliningrad), and Kaunas to Riga. The third part from Berlin was sent through Frankfurt on the Oder, Wrocław, Opole, Bytom, Katowice, Kraków, Lviv, Stanylsaviv, and Chernivtsi to Bucharest.
The interwar Polish State Railways had no need to be ashamed of the speed of transport. Trains pulled by steam locomotives were allowed to develop the highest speed – 68 mph (110 km/h) – on the section from Poznań to Zbąszyń. Trains travelled at 62 mph (100 km/h) on the Łapy – Białystok – Hrodna – Vilnius route and on the route from Warsaw to Radom. On the other hand, “rail car” sets could reach 75 mph (120 km/h) on the route from Warsaw to Katowice, Łódź Fabryczna, Łapy and Poznań. Their commercial speed at the Warsaw – Koluszki section was up to 59.5 mph (95.8 km/h). At the end of the interwar period the fastest train was the Nord Express whose route was extended to Moscow. Its commercial speed at the Zbąszyń – Poznań section was 58 mph (93.4 km/h), and on the Warsaw – Stołpce section 52.6 mph (84.6 km/h). It took 7 hours and 15 minutes for the train to travel from Warsaw to Berlin.
An important project completed in the interwar period was the construction of the Warsaw Main Railway Station (1931 – 1939) above 8 tracks laid in a cut. The design by Professors Czesław Przybylski and Andrzej Pszenicki provided for a steel, riveted structure with a reinforced concrete slab over the tracks.
The slab was to be the foundation for 130 x 85 m buildings with a 26-metre-tall main departures hall and a 14-metre-tall arrivals hall connected by a five-storey office building.
Thanks to organisational efforts in less than 20 years it was possible to introduce efficient railway authorities and services, integrate separate systems of transport created by 3 disparate occupying forces in the past, set up a national rolling stock industry, educate railway staff, reconstruct and improve the technical condition of railway lines, increase train speed and achieve high degree of punctuality of trains.
Railwaymen were a strong occupational group in which engine drivers were regarded as the elite. The Polish State Railways had 16 trade unions in addition to self-help associations such as, for example, Rodzina Kolejowa (the Railway Family). Industry magazines were issued for respective services. In Technika Parowozowa (Steam Locomotive Technology), a supplement to Maszynista (The Engine Driver – published by the Engine Drivers' Trade Union), in 1929 the competition for the most beautiful PKP steam locomotive was announced. The winner was Ok22, since the voices in support of her beauty, emphasized her grandness and looks; a beautiful design makes a harmonious whole; 3 tied wheels, 2 bogie wheels in an assembly with a delicate mechanism (trailing and steam valve) are a fine view; a shapely smoke-box, a pretty narrow tank and sander, proportional short funnel, beautiful slanted booth, and lovely paint coat enhance her beauty, excellent location of the boiler and effective performance. These words prove that railwaymen really loved their engines.
However, not all things were so beautiful. The failed but costly purchase of 3,300 sets of the French Pyram instruments for smokeless combustion of coal in steam locomotives echoed strongly in 1935. The equipment cost 35 million francs and it took another million to install them. The units feeding steam to the furnace (decreasing the share of air in the combustion of coal) and to the smoke-box (to prevent sparks), were in addition supposed to save fuel. The operating principle was similar to that of the Langner equipment used on a small scale, but the degree of automation was higher. The fallible, expensive and unreliable equipment that was difficult to operate did not improve the quality of performance of steam locomotives or allow coal savings.